Rough Idle when in Drive and stopped only

[Chowda]

Ok I’m at a loss and turning to the experts.

I have an 87 K5, 350 TBI, 700R4.

Idles nice and smooth when in park and in Nuetral but when sitting at a stop light she’s no bueno. Starts feeling very rough just sitting there while in drive. If I shift it into nuetral then all is well in the world. Have to wait to until cars move and then I shift back to drive and shifts fine and drives fine.

I read in a different forum it could be the IAC. Figured before I started throwing good money away I would see if anyone else has had this problem.

I should mention it has new plugs,wires, cap/rotor, PCV Valve and air filter.

Thanks in advance.

Marc

 

[Wes Harden]

check for vacuum leak, intake, hoses, and tbi base gasket. IAC plunger could be coked up limiting the air at idle. look at injector spray for nice cone shaped spray. Last time fuel filter was replaced ?

 

[dyeager535]

GM's IAC is exceptionally robust IMO. I don't know as I've heard of more than say 5, in all my years online, that had actually failed. Tons replaced (just like ECM's) very few the culprit.

Second the above...vacuum leaks, or misconnected vacuum lines. Do a very thorough underhood inspection...all wiring, hoses, fittings, connections, etc.

 

[Chowda]

Thanks Wes,

I’ll check for a vacuum leak and the TBI gasket. The fuel filter, fuel pump/strainer and sending unit are brand new.

Marc

 

[Chowda]

Thanks for the response, I’ll check everything and report back. Hopefully it’s just a lose connection somewhere.

 

[Williebeaman]

Does your truck ever die in reverse? You sound similar to my problem (rough idle/ dies when I put in reverse sometimes if I don’t slam the gas pedal fast) so far over done pcv/egr/vacuum check valve/ rebuilt tbi all new gasket. I stilll can’t find my problem yet.

 

[Chowda]

Williebeaman,

It has not died in reverse yet but truth be told I am just getting it back on the road from doing some major work to it. To include inner/outer rocker panels and some flooring. Soooo I am at the beginning of finding this problem. However it has not died in reverse, yet

 

[nbrown2500]

I would also check to see if the butterfly in the TBI is seating all the way. Sometimes they wobble in the TBI when the shaft is loose. Just saying, mine is loose and sometimes causes the same problems. I need to have bushings installed in it.

 

[Williebeaman]

Williebeaman,

It has not died in reverse yet but truth be told I am just getting it back on the road from doing some major work to it. To include inner/outer rocker panels and some flooring. Soooo I am at the beginning of finding this problem. However it has not died in reverse, yet

I just replaced my o2 sensor and so far I haven’t stalled out! My problem wasn’t constant though so idk for sure if it fixed the problem but time will tell. My old one looked like it might have been the original lol.

 

[Wes Harden]

O2 sensor do get used up, they are a chemical battery. I would have expected a check engine light and a fuel system always command rich or lean code.

 

[Williebeaman]

Well it stalled on me again so not the o2 sensor. Idle air control valve next, and new vacuum lines after that I suppose one thing at a time.

 

[dyeager535]

Iac can be pulled and cleaned. IAC works under more conditions than just idle, I'd expect to see some issues besides just stalling if it were the culprit.

Egr, vss, vacuum leaks, low fuel pressure, sticky tcc solenoid (not sure if 700 tccs do this like the fwd gm trans of the same era did) all potential sources of stalling.

 

[Chowda]

I dropped my rig off for paint so it will be a couple weeks before I can really start trouble shooting this.