Loopy idle

[Texvet]

1992, 5.7, SCLB, 1500, 2WD

I finally worked through my no start issue. I also replaced the MAP sensor because the 33 code showed up after it left me stranded. I don't think the MAP sensor had a role in the no start. But replaced it because it thru a code.

The truck runs as it should.... Except it has a bouncy idle at cold start. I does it for 30 seconds or so, then smooths out steady at 700 rpm - until I put it gear - then it stumbles again, bouncing it 1000 - 1500, then settles in at 550 - 600 (in gear). Acceleration is good/normal. Half the time when I come to a stop it bobbles/stumbles but hasn't stalled because throw it into neutral. Then it goes back to a steady idle.

I pulled the IAC to see if it was dirty. It was clean as a whistle. Timing is right on the 0 degree mark.

What are your thoughts?

 

[b454rat]

Clean the EGR valve? I had one with a plugged/dirty one, sounded like a pro stock idling lol....

 

[Texvet]

Clean the EGR valve? I had one with a plugged/dirty one, sounded like a pro stock idling lol....

I did check to see that it held vaccumn today, but didn't pull it to look for carbon build up. I'll check it.
Thanks,

 

[frito-bandito]

If that doesn’t work, check the distributor shaft for play. Distributor gear wear is pretty common on these trucks.

 

[Tim W]

My truck did that too when it had the stock tbi 350. I did everything you did to try to fix the problem (at first) but learned to live with it when nothing worked. I went as far as replacing my EGR valve, cap and rotor. I didnt want to spend the money on plugs and wires because i knew this engine was going to be removed soon.

To be honest I didnt mind it bc i like a choppy idle. I knew it wasnt right but i was having an engine built so i didnt care to much.

Come to find out my timing chain had some slop in it. Dont know if that was the cause or not but thats the only thing I could find. Keep in mind im far from being a mechanic so im sure it was something else.

 

[Texvet]

I hear what your saying. I wish a rebuild or new motor were in the cards for me.

It is worst on a cold start, after it gets to operating temp it only does it half the time (at idle). I don't notice it at all above an idle. Not to say it isn't doing it? But the tach does not bounce like it is. In fact the truck seems to run great.

I am wondering if the IMC I installed to fix the no start issue it's working as it should? It came from AZ and from what I read they are boarder line junk?

Worst part is I don't feel like I can trust it - just waiting for it leave me stranded again!!!

 

[PlayingWithTBI]

Just for ***** and giggles, try spraying some water on your coil, not the wires, while idling and see if it stumbles.

 

[Texvet]

I sprayed it, and it stumbled like an old drunk!

 

[PlayingWithTBI]

Good you found it! Now you just need to verify the coil didn't hurt the ICM too. Get good quality parts like AC Delco, Delphi, etc.

 

[Texvet]

Thank you for your insight.

So - I should get a good quality coil and see if it runs OK?

I don't know of any parts houses that test ICMs. That is to say - the big chains don't. I asked the guy AZ if they test ICMs, and he looked at me like I had two heads....