[e90yyc]

When I start my 328, the idle is fairly uneven for the first 30 seconds give or take. Happens only on cold starts. Once it settles out everything is fine.

• At no point does the car feel like it's going to stall.
• Sometimes the engine will rev a bit almost as if I've applied throttle. Nothing crazy, just a rise of maybe 200 rpms for a few seconds.
• It doesn't "bounce," it's more just high and uneven.
• Once the engine is warm and the idle settles, it still feels a bit coarse on my butt in the seat. Maybe this is normal, but I do have brand-new engine mounts, so I'd expect it to be a bit smoother.

I performed a smoke test, but frankly it was inconclusive. I saw a tiny tiny amount of smoke seeping from one of my DISA valves, but this issue has existed long before I did my 3IM swap. When I removed the smoke tester from the intake, there was an audible pressure change, which leads me to believe that if there is a vacuum leak it's extremely minor. This plus the fact the issue only seems to occur on cold start (open loop) and never when (presumably) running in closed loop leads me to believe it might not even be vacuum related at all.

No codes, no other obvious signs of failure. Only thing that comes to mind is my rear main seal which I think is leaking. Won't know for sure until I pull my transmission (manual swap!), but even if it is leaking I doubt it would be enough to cause what I'm feeling. (Then again I also don't have a fucking clue what I'm talking about which is why I'm asking for help, lol.)

Any ideas? I will take a video and upload it here soon in case it offers any clues. Thanks!

[lowrydr310]

Sounds just like a small air leak to me. Engine is much more sensitive to air at idle RPMs than it is under high RPMs. I had similar uneven idle on cold starts, and a few times the idle would bounce immediately after coming to a stop. Eventually the SES light was set with lean codes. It ended up being a cracked CCV hose, something that failed before and the previous owner tried to fix with flex tape, and eventually the flex tape failed.

Did you ever fix that broken bolt on your intake manifold?

If you're seeing smoke leak out of the disa flap seal that could be just enough of a leak to mess with the idle.

[e90yyc]

Originally Posted by lowrydr310

Sounds just like a small air leak to me. Engine is much more sensitive to air at idle RPMs than it is under high RPMs. I had similar uneven idle on cold starts, and a few times the idle would bounce immediately after coming to a stop. Eventually the SES light was set with lean codes. It ended up being a cracked CCV hose, something that failed before and the previous owner tried to fix with flex tape, and eventually the flex tape failed.

Did you ever fix that broken bolt on your intake manifold?

If you're seeing smoke leak out of the disa flap seal that could be just enough of a leak to mess with the idle.

Thanks! Good to know that even a tiny leak could cause this.

Only reason I don’t believe it’s related to sheared intake bolt or DISA valve is that the issue was around long before either of those two things were. I also did manage to tighten down manifold bolt even with butchered threads.

Maybe it is the RMS??

I could try smoke testing again with no underbody panels and slide under the car. I didn’t do that the first time.

[hassmaschine]

Cold start / idle is actually one of the most difficult parts to tune. Anyone can tune for WOT power, but a perfectly smooth cold start/idle takes a team of engineers to really nail.

That's why I never mess with any of the "cold" maps of the OE tunes - and even then, you can have "odd" stuff like this, especially if there are any mods.

Honestly, unless you're having an actual problem, codes, roughness when warmed up - I wouldn't worry about this one bit. I kind of feel that way every time I see one of these "cold start isn't perfectly smooth" threads, because the reality of cold starts, is they are never perfect - although the OE tunes get it closest.

I've built several standalone computers and tunes from the ground up - the thing I spent way, way more time on anything was always cold starts. If it starts up the first try, every time without issue, but maybe the idle wobbles a bit for a few seconds - I'd call that a win!

[tgeho_e92]

Originally Posted by hassmaschine

Cold start / idle is actually one of the most difficult parts to tune. Anyone can tune for WOT power, but a perfectly smooth cold start/idle takes a team of engineers to really nail.

That's why I never mess with any of the "cold" maps of the OE tunes - and even then, you can have "odd" stuff like this, especially if there are any mods.

Honestly, unless you're having an actual problem, codes, roughness when warmed up - I wouldn't worry about this one bit. I kind of feel that way every time I see one of these "cold start isn't perfectly smooth" threads, because the reality of cold starts, is they are never perfect - although the OE tunes get it closest.

I've built several standalone computers and tunes from the ground up - the thing I spent way, way more time on anything was always cold starts. If it starts up the first try, every time without issue, but maybe the idle wobbles a bit for a few seconds - I'd call that a win!

Originally Posted by hassmaschine

Cold start / idle is actually one of the most difficult parts to tune. Anyone can tune for WOT power, but a perfectly smooth cold start/idle takes a team of engineers to really nail.

That's why I never mess with any of the "cold" maps of the OE tunes - and even then, you can have "odd" stuff like this, especially if there are any mods.

Honestly, unless you're having an actual problem, codes, roughness when warmed up - I wouldn't worry about this one bit. I kind of feel that way every time I see one of these "cold start isn't perfectly smooth" threads, because the reality of cold starts, is they are never perfect - although the OE tunes get it closest.

I've built several standalone computers and tunes from the ground up - the thing I spent way, way more time on anything was always cold starts. If it starts up the first try, every time without issue, but maybe the idle wobbles a bit for a few seconds - I'd call that a win!

I've made a few threads asking about similar problems. This made me feel A LOT better about my cars cold starts. I'll keep a close eye on this thread though for any more input.

[e90yyc]

Originally Posted by hassmaschine

Cold start / idle is actually one of the most difficult parts to tune. Anyone can tune for WOT power, but a perfectly smooth cold start/idle takes a team of engineers to really nail.

That's why I never mess with any of the "cold" maps of the OE tunes - and even then, you can have "odd" stuff like this, especially if there are any mods.

Honestly, unless you're having an actual problem, codes, roughness when warmed up - I wouldn't worry about this one bit. I kind of feel that way every time I see one of these "cold start isn't perfectly smooth" threads, because the reality of cold starts, is they are never perfect - although the OE tunes get it closest.

I've built several standalone computers and tunes from the ground up - the thing I spent way, way more time on anything was always cold starts. If it starts up the first try, every time without issue, but maybe the idle wobbles a bit for a few seconds - I'd call that a win!

Appreciate the input.

True haha. Since it seems to be doing it more lately I thought maybe there is something "fixable" haha.

I'm not too bothered by it so I'll just leave it be. Definitely nowhere near as annoying as the shaking I still have yet to solve (lowrydr310 )

[Glene]

From my experience, idle fluctuates during cold start (and not happens when engine warmed up) is usually due to leaky injector(s). The engine sits for awhile, gas leaks into the combustion. During cold start, computer tries to adjust to extra fuel causing engine to fluctuate for few seconds then stabilizing down. In this case, it won't set any code.

[Mantraxalos]

Originally Posted by Glene

From my experience, idle fluctuates during cold start (and not happens when engine warmed up) is usually due to leaky injector(s). The engine sits for awhile, gas leaks into the combustion. During cold start, computer tries to adjust to extra fuel causing engine to fluctuate for few seconds then stabilizing down. In this case, it won't set any code.

If this was the case, do you think the EASIEST test would be to just pull the entire fuel rail and pressurize the system? At that point just look for any drips. Or are there better, more accurate methods?

[Glene]

Originally Posted by Mantraxalos

If this was the case, do you think the EASIEST test would be to just pull the entire fuel rail and pressurize the system? At that point just look for any drips. Or are there better, more accurate methods?

If it's my personal car, I'd add marvel mystery oil to the gas tank and run it for couple of tanks, this may smooth out the fluctuating condition. I've been using MMO for the last 20 years and have good results.

[e90yyc]

Originally Posted by Glene

From my experience, idle fluctuates during cold start (and not happens when engine warmed up) is usually due to leaky injector(s). The engine sits for awhile, gas leaks into the combustion. During cold start, computer tries to adjust to extra fuel causing engine to fluctuate for few seconds then stabilizing down. In this case, it won't set any code.

I think we have a winner.

Whenever my car is not asleep (such as when I’m working on it), it seems to prime the fuel pump more frequently than I would expect. Now, I don’t know what’s normal, so would first need to hear how often other’s cars prime the system before knowing.

Could I put a pressure gauge on the rail and watch for drop?

[lowrydr310]

I thought the N52 injectors were robust and not likely to fail. I know there's always that off chance but for the most part you don't hear about injector failures on these engines. There are a lot of high mileage N52 owners on this forum with original injectors - I am one of them. On that car (325) I had some fluctuating cold idle issues that I didn't bother to fix but eventually resolved by sealing a punctured evap purge return line from the canister up to the intake manifold. I think I also ran a bottle of Techron and later Marvel Mystery Oil in the gas tank over a few months too.

I'm not saying it's wrong to inspect/test injectors, it's just not common and there are usually other things to inspect first, like the air leaks. I'll definitely be following this thread to hear the outcome since I like to be educated for any issues I may encounter with my car.

I also see a lot of posts of people complaining about a "crank no start" condition and someone chimes in that their buddy Jimbo who works on Jeeps replaced the fuel pump for him and it didn't fix the problem. (N52 fuel pump housings DO crack and leak fuel, but the pump itself doesn't usually fail)

[e90yyc]

Originally Posted by lowrydr310

I thought the N52 injectors were robust and not likely to fail. I know there's always that off chance but for the most part you don't hear about injector failures on these engines. There are a lot of high mileage N52 owners on this forum with original injectors - I am one of them. On that car (325) I had some fluctuating cold idle issues that I didn't bother to fix but eventually resolved by sealing a punctured evap purge return line from the canister up to the intake manifold. I think I also ran a bottle of Techron and later Marvel Mystery Oil in the gas tank over a few months too.

I'm not saying it's wrong to inspect/test injectors, it's just not common and there are usually other things to inspect first, like the air leaks. I'll definitely be following this thread to hear the outcome since I like to be educated for any issues I may encounter with my car.

I also see a lot of posts of people complaining about a "crank no start" condition and someone chimes in that their buddy Jimbo who works on Jeeps replaced the fuel pump for him and it didn't fix the problem. (N52 fuel pump housings DO crack and leak fuel, but the pump itself doesn't usually fail)

You are correct as far as I know, which is why I didn’t even consider this as a possibility. I will try running some mystery oil through for a couple months, and if I can get my hands on a pressure gauge for a decent price I will check rail pressure with engine off.

I’m going to take another look at my vacuum system. I haven’t been able to find a diagram that shows everything, so if anyone has a link that might help please post it.

[PhaseP]

Originally Posted by Glene

From my experience, idle fluctuates during cold start (and not happens when engine warmed up) is usually due to leaky injector(s). The engine sits for awhile, gas leaks into the combustion. During cold start, computer tries to adjust to extra fuel causing engine to fluctuate for few seconds then stabilizing down. In this case, it won't set any code.

You have 335 with high pressure injectors. N52 injectors are not known to leak. For all those years I have been in this form I remember only one post that someone really had a problem with N52 injectors that got fixed by replacement.

[PhaseP]

Originally Posted by e90yyc

Could I put a pressure gauge on the rail and watch for drop?

Yes you can, but if you see dropping pressure, it may indicate leaking injector(s) or the the fuel pressure regulator is not holding the pressure after shut down. The fuel pressure regulator is part of the fuel filter that is inside the fuel tank.

I had fuel pressure regulator slowly loosing pressure after shut down. The symptom was that it took long cranks to start after car sat down. But once started idle was fine.

Computer tries to compensates such issue (too lean or too rich) by either reducing or increasing the injected fuel up to %20. If the correction needed goes beyond that it throws too lean or too rich error, engine light will come up.

You can try to look at the sensor readings and etc via INPA, it may give some insight to what is going on. They are not easy to interpret, and it had been long time I had looked at those myself when chasing idle plus loss of power issues on mine, so I can't remember which screen and what to look for.

[e90yyc]

Originally Posted by PhaseP

Yes you can, but if you see dropping pressure, it may indicate leaking injector(s) or the the fuel pressure regulator is not holding the pressure after shut down. The fuel pressure regulator is part of the fuel filter that is inside the fuel tank.

I had fuel pressure regulator slowly loosing pressure after shut down. The symptom was that it took long cranks to start after car sat down. But once started idle was fine.

Computer tries to compensates such issue (too lean or too rich) by either reducing or increasing the injected fuel up to %20. If the correction needed goes beyond that it throws too lean or too rich error, engine light will come up.

You can try to look at the sensor readings and etc via INPA, it may give some insight to what is going on. They are not easy to interpret, and it had been long time I had looked at those myself when chasing idle plus loss of power issues on mine, so I can't remember which screen and what to look for.

Thanks!

My plan at this point is to pull the fuel rail/injectors and then run activation of fuel pump using ISTA (which runs it for 20s). I figure if there is a leaking injector I will see it.

[Mantraxalos]

I just helped my cousin change the pressure regulator on her 08 E92 N52 154k mi. The month prior cylinder #1 kept misfiring. That was tracked down to a failed injector. We never inspected to see if it was leaking. Just looking at the bottom of all the injectors and seeing 5/6 all shiny silver in appearance. Injector 1 was brown, so we changed it out and the engine was running smooth again.
A few weeks later she started having long cranks and smelling a strong odor of fuel after shutting down the engine. We lifted the rear driver side seat, and unscrewed the four 10mm nuts of the pressure regulator access cover. Under that access panel was all wet with petrol. The regulator was changed and her car is now running great again. She continues to always drive it until empty, so I'm sure issues will reappear in the near future.

Originally Posted by PhaseP

Yes you can, but if you see dropping pressure, it may indicate leaking injector(s) or the the fuel pressure regulator is not holding the pressure after shut down. The fuel pressure regulator is part of the fuel filter that is inside the fuel tank.

I had fuel pressure regulator slowly loosing pressure after shut down. The symptom was that it took long cranks to start after car sat down. But once started idle was fine.

Computer tries to compensates such issue (too lean or too rich) by either reducing or increasing the injected fuel up to %20. If the correction needed goes beyond that it throws too lean or too rich error, engine light will come up.

You can try to look at the sensor readings and etc via INPA, it may give some insight to what is going on. They are not easy to interpret, and it had been long time I had looked at those myself when chasing idle plus loss of power issues on mine, so I can't remember which screen and what to look for.

[e90yyc]

Originally Posted by Mantraxalos

I just helped my cousin change the pressure regulator on her 08 E92 N52 154k mi. The month prior cylinder #1 kept misfiring. That was tracked down to a failed injector. We never inspected to see if it was leaking. Just looking at the bottom of all the injectors and seeing 5/6 all shiny silver in appearance. Injector 1 was brown, so we changed it out and the engine was running smooth again.
A few weeks later she started having long cranks and smelling a strong odor of fuel after shutting down the engine. We lifted the rear driver side seat, and unscrewed the four 10mm nuts of the pressure regulator access cover. Under that access panel was all wet with petrol. The regulator was changed and her car is now running great again. She continues to always drive it until empty, so I'm sure issues will reappear in the near future.

Good to know. Thanks!

Does anyone know how often they hear their fuel pump prime with the car off?

[PhaseP]

Originally Posted by e90yyc

Good to know. Thanks!

Does anyone know how often they hear their fuel pump prime with the car off?

I don't remember it is priming with regular intervals. But I had noticed if I open the door to get back in the car after it was turned off for some time, I hear the fuel pump prime, to make the engine ready to start up.

I think your most likely culprit for idle rpm is some vacuum leak though. Any possibility you have a crack on the valve cover, or torn PCV valve membrane?

[e90yyc]

Originally Posted by PhaseP

I think your most likely culprit for idle rpm is some vacuum leak though. Any possibility you have a crack on the valve cover, or torn PCV valve membrane?

It’s possible, but wouldn’t that show up with a smoke test?

Not sure how to check for PCV valve membrane. Will look into that tomorrow. Thx!

[mainbearing]

I do not recall ever hearing the fuel pump priming on the E90, whereas with Audis opening the driver side door primes it. I will keep an ear out for it.

Originally Posted by e90yyc

Good to know. Thanks!

Does anyone know how often they hear their fuel pump prime with the car off?

[mainbearing]

If the rail and injectors are pulled and you activate the pump, wouldn't the injectors shoot off?

Originally Posted by e90yyc

My plan at this point is to pull the fuel rail/injectors and then run activation of fuel pump using ISTA (which runs it for 20s). I figure if there is a leaking injector I will see it.

It should unless it's a tiny pin hole. Another might be whistling sound.

Originally Posted by e90yyc

It’s possible, but wouldn’t that show up with a smoke test?

Not sure how to check for PCV valve membrane. Will look into that tomorrow. Thx!

[e90yyc]

Originally Posted by mainbearing

If the rail and injectors are pulled and you activate the pump, wouldn't the injectors shoot off?

It should unless it's a tiny pin hole. Another might be whistling sound.

Good question, but not if I just activate the fuel pump using ISTA or INPA. Alternately I could crank the engine with the connectors injector harnesses unplugged so they don’t shoot their fuelly load in my face.