Hi everyone

I am trying to diagnose some running issues with my 1988 coupe, that started about 2 weeks ago.

So, from one day to another the car started to run very rough when cold to the point when it would struggle to take off from a stop sign. It would initially start and then die immediately, and finally stay running after the second or third attempt but ran very rough.
At first it looked like when my fuel pump hit the dust so I hooked up a pressure gauge that showed everything normal (both static and dynamic), no leaks when ignition switched.

I hooked up my computer with tuner pro and none of the sensor readings looked absolutely crazy the only thing back when it was running very rough, the IAC was open to the max (around 144) and the intake vaccum was around 15 in. I plugged and unplugged the MAF, and it seemed to be running a tad better with the MAF unplugged, but unconvincing.

I looked at the usual suspects: egr valve (fine), checked the torque on the runner bolts and intake bolts I could reach. All checked out ok. The gaskets are maybe 3 years old so I don't think there's any significant vaccum leak. The idle speed had been adjusted a few years ago when I replaced the and everything ran very well until two weeks ago.
I also replaced the spark plugs for good measure since I had a bunch lying around and they were 4 years old.

So anyway after doing this initial check, and forcing the engine to run rough for a bit it eventually starting running and driving better. To the point where I drove to gas station and refiled the tank (about 10 gals) and it ran even better. I figured this might have been contaminated fuel and put a bottle of iso-heet water remover just in case. After that the intake vaccum at idle was better (around 18in) even when cold.

So today still idles roughly in open loop but admittedly way better than two weeks ago, and the close loop seems fine, except for a high BLM

Here are the reading today on tuner pro at idle in parkCoolant 200
Rpm 675
Int 131
BLM 152
Iac position 16
MAF 5.93 g/sBase pulse width 1.88 ms
I did another run later and got an even higher BLM (160) at the same RPM, but the MAF was reporting less airflow (5.6 g/s).
TL;DR I find the maf reading a bit low for this idle speed (I have read numbers around 7g/s here and there), but that could also be caused by a air leaks.
any opinions? Advice?

Thanks!

 

Bumping the thread.
anybody has experience with a car suddenly running like s*** and kinda fixing itself?
Thx!

 

MAF relays can cause skewed readings. Egr valve not fully seating.. TPS reading? Does O2 reading bounce from under .10.to over .90 ?

 

Just wanted to give an update, after smoke testing and replacing the 2 years old oxygen sensor it turned out the problem was the MAF. A new Delphi unit made the engine run like a champ!

Now the car is apart as I am getting the steering rack and ps pump rebuilt by Turn One 🥳 and I am expecting a Corsa exhaust to make it sound even better.
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