I have been looking into why might engine seems to have a rougher idle than usual. Apart from other things I am looking at, the engine recently developed this. When you start it cold, it fires and then idles very low,almost stalling, but after a few seconds it will rev up over 1000.

Also when it is cold, during the first minute of running, if you blip the throttle, you can almost get a back fire or pop.

I am suspecting my timing circuit somewhere.


When the engine is warm with my rough idle, if I disconnect the set timing plug, it idles smooth. When reconnected it is rough. You can watch the timing move 2-4 degrees at idle. Seems odd to me.


No codes. I had replaced the IAC a month ago.

Does this sound like a knock sensor that is going bad?
OR how about the ESC? Although the ESC seems like it would have other symptoms.


If anyone has a moment to share some thoughts, I'd appreciated it.

Mark.

 

ttt

I'd like to nkow the answer to this also. Anyone have any ideas?

 

While this does not answer the question, it does show some of the things I have been looking into:

https://www.thirdgen.org/techbb2/sho...hreadid=127625

The engine still surges when warm. I've checked many things, but still have not found it. Apart from replacing things that I can't test (HEI module, ESC, etc.), I am rather baffled.

My thoughts are that I have a sensor or a group of sensors that our just out of spec or out of range. It seems that it is fuel or spark related.

I have another distributor (complete) ... perhaps that is something to try.

Mark.

 

Hi, I'm new to this board. What was wrong with your car. My car is doing the same thing. I have a MCSS with a Vortec head 350 out of 89 formula. Thanks for you help in advance.

 

Check the distributor shaft to see if it's coming separated from the reluctor wheel. Mine did this at 125,000 miles and caused these same symptoms. Luckily I got it before the shaft completely separated or I would of been stranded somewhere.

 

Mike,

When you say it is seperating what is seperating? Is the reluctor wheel comming loose from the shaft and thus allowing some movement in the position of wheel?

I know my dist has a few miles on it. I'd like to know where to tug/pull to see if anything is loose. I have a spare on the bench to rebuild if that is the case.

Mark.

 

Exactly, it's where the shaft meets the reluctor wheel. It's like a pressed on type connection and over time I guess it just corrodes away. If you turn the wheel with the distributor cap off you might be able to tell if it's gotten really bad. Might be easier with it out of the car though..

 

Hey Mark, don't know if you remember my post a few weeks ago about trying to set my idle and get the IAC counts down some at idle, but mine is surging now at idle and just about all through the rpm/load ranges...sometimes. Other times it seems to run fine. It never does it at WOT though when the ECM is not in Block Learn Mode. It sometimes does it in OPEN Loop. I was thinking O2 sensor, thats why I've ordered a new, per my other post. But the one thats in there is only about 2 years old and has about 15k on it, they should last a lot longer than that, but I ran it for a year pig rich before I started burning my own chips.
Anyway, it seems to be getting worse as time goes on, and its again running very rich according to the BLM numbers on my scan tool, I had them perfect for a while before this problem cropped up.
I should get the O2 in a few days, after that, I'm going for a new set of injectors, thinking I may have one not functioning properly, but by looking at my plugs, all looks normal, but like I say, it doesn't do it all the time, and some days worse than others...
My distributor was brand new also 15k miles ago so I'm ruling out the loose timing reluctor on mine.

 

2Quik6,

I know how you feel. Mine too seems to be getting worse with time. I've check and replaced many things, but it is still there.

I also suspect my injectors. Perhaps at low RPM, they are flowing poorly. But I tried to up the pressure, and even run with the regulator disconnected from vacuum, and no change. I would have suspected something.

I'm now looking at the odd things such as the dist.

My O2 is as well 2 years olds. I would not suspect it to be the problem, but when I disconnected it (after the engine was warm) the surge got worse! So it makes me think the problem is fuel related.

MArk.

 

Well Mark, I disconnected my O2, don't have a new one yet, and so far, 1 trip to the auto store, and no surging. Its was near dark when I disco'd it but it appears that maybe the wire were right pulled tight against a sharp metal/tin heat shield from the tranny, possibly cutting the wires, I'll look tomorrow in the light.
I'll drive it to work disco'd and if it doesn't surge on the highway, then I think I found my problem. But have more question about runnin it disco'd now....

 

Well, on the way to work, it runs perfect while giving it any amount of throttle. But at idle, it surges worse sometimes. Have to be certain I have the brake applied fully at each stop light or I may bounce upon the car in front of me. It surges from 600 to 900 rpms very quickly.
Rich at Cruizinperformance told me the original injectors, (the black and gray/silver ons) are junk and are not worth servicing and have the highest failure rate. These were the factory injectors on the 90-92 TPIs.
With that said, I suspect I have a screwed up injector that not stuck all the time, but sticks some of the time, messing up idle smoothness, and then at part throttle, its leaking in enough extra fuel to fool the O2 thats its running rich so the ECM is cutting fuel to the extreme the other cyclinders become lean, causing the surging at part/cruise throttle.
My BLMs at cruise will sometimes be right on at 126-130 when its running good, and then at the times its surging, they are at 110-114!! at the same rpm and MAP.
*
I think if it were timing related, I'd still see the problem with the O2 hooked up in CLOSED LOOP.
Anyway, based in Rich's opinion of the stock injectors, and my suspisions, I'm going to purchase a set of Accel 24# injectors and go from there, I'll let you know how it turns out, but it may be several weeks before I get there...