2.7i rough idle and intermittent hard starting

[dumpski88]

My car won't idle after the 2.7i swap but runs fine I have seta bottom and an I head with I injectors and intake manifold and I maf but I did put some cheap headers on and It didn't have a spot for the o2 sensor so that could be the problem.

[SmokeE30]

My car seems to idle a bit rougher after going 2.7i but I'm pretty sure it's just vacuum leaks. A lot of stuff gets disturbed durring the swap I have no doubt that something won't seal right and will require attention after a heat cycle or two on most peoples cars. Heck the first one I ever built with a buddy back in college picked up 8 in of vacuum just from retorqueing the intake manifold bolts after a couple drives.

[david2991]

I just finished the 2.7i install and I am having the exact same issue. I replaced all gaskets and intake components which leads me to believe I should be looking at a fuel issue. Maybe the injector or fuel regulator or pump. Either way...subscribed. Let ya know if I diagnose it.

[e30jake]

Finally did a homemade smoke test. Was leaking a lot from one of the elbows on the throttle body that connects to the hose to the brake booster. It was the only place I could really tell smoke was coming out of due to the wind blowing it everywhere. Sealed it up and went for a drive today and it feels good. I also may have fixed the idle dip by adjusting the throttle plate, although it could have just been that the car warmed up. It feels good, but it still doesn't sound great. If I put my hand by the exhaust I can feel intermittent puffs of air, rather than a steady flow. Is this somewhat normal? I have also checked 2 of my friend's e30s. The 86 e was similar to mine, with little puffs hitting your hand. It has been driven like this for years. The 90 i was a smooth air flow, which leads me to believe my car could be running smoother. Anyone have any input on this?

[e30jake]

Replaced this hose today. Not sure if it actually helped or if it was a placebo effect, but it did seem a little better. It hasn't started hard since I last posted. I have had the CEL come on for 1 or 2 seconds every once in a while when I am driving, but it immediately goes back off. I also still have the problem of the idle dropping to ~500 rpm sometimes when I come off the gas or put the clutch in before settling back to around 750 rpm. It definitely seems worse when the car is cold, almost sounding like it is about to die completely. It did this even before I did the head gasket and head swap, which narrows it down to something I re-used. Would a dirty ICV cause this? All electronics tested fine from the ECU plug according to the Bentley tests other than the TPS at full throttle, which wouldn't be related to my idle. Still need to get around to doing DIY smoke test, but I'll keep screwing around with it and seeing if anything changes until then.

[e30jake]

+1

c191 plug can get corroded and cause all kinds of weird symptoms that can mimic multiple issues. Worst of all, it can be intermitent making it harder to diagnose. It's directly under the intake, round plug that screws together. There have been a few recent threads on this topic. Search for c191 and look at threads within the last month.

I actually tried cleaning the c191 plug before with some wd40 but it was hard to get inside. My threads are messed up which makes it hard to plug and unplug it repeatedly. Maybe ill just pick up an extra injector harness at the yard. Anyone know if the early and late injector harnesses are the same?

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[603Racing]

Does sound like an injector issue, the stock seta injectors will work to test if that's your issue. Also check the wiring to the injectors including the c191 i believe it's is under the intake manifold connecting the injector harness to the rest of the engine harness.

+1

c191 plug can get corroded and cause all kinds of weird symptoms that can mimic multiple issues. Worst of all, it can be intermitent making it harder to diagnose. It's directly under the intake, round plug that screws together. There have been a few recent threads on this topic. Search for c191 and look at threads within the last month.

[e30jake]

A real smoke machine? That's a lot of $$$. I'll try DIY smoke machines first, cheap, and easy to make.

That's what I meant. One of the cheap ones. If I had the dough for a real one I would just be paying someone else to figure this out lol

[dnguyen1963]

A real smoke machine? That's a lot of $$$. I'll try DIY smoke machines first, cheap, and easy to make.

[e30jake]

Tested all the sensors at the ECU plug. Everything read what it was supposed to except the TPS at full throttle, which wouldnt effect the idle (right?) It seems more and more like a vacuum leak. If I unplug the vacuum line from the inake manifold to the FPR nothing changes, which doesnt seem right. I have replaced the FPR with a known working one without any changes. Along with rough idle, it also starts hard sometimes for seemingly no reason at all. Warm or cold outside, warm or cold engine, doesnt matter. I already cleaned the four main grounds. Not really sure what else it could be, but it never did this before the head swap. I have also noticed a major hesitation/bogging every once in a while when Im driving it. Throttle goes in, nothing happens except for a little bit of the car shaking, then it starts to pull. Usually happens between 1500 and 3000 rpm. I am planning on buying a smoke machine to do a home smoke test in the near future. Anyone have any other ideas?

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[bmwstudent]

what do you mean "no"

the fuel rail is a hollow piece of metal, if it was only half full there wouldn't be any pressure in it.

[Mr. Tasty]

no

what do you mean "no"

[e30jake]

First post updated

[e30jake]

Didnt have time to work on it until this afternoon. Jlevie was spot on (as usual.) Put my old injectors back in and everything is all good. I guess the i injectors i got were bad. Glad to finally have it done

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[bmwstudent]

is it only running off the first three cylinders closest to the firewall? Maybe a fuel pressure issue and fuel is only getting that far down the fuel rail?

no