Anyone ever adjust the idle speed on a 94 Jimmy (the little one) with the 4.3l?

Just picked one up from the FIL and it BARELY passed the emissions test. 218ppm out of 220ppm allowed of HC. Gota a small miss at idle but the idle is down near 600 rpm I figure that's a bit low and a 50rpm increase makes the miss all but dissappear.

All other emissions #s are good by a long shot so I'm not worries too much about it but I would like to make it idle smooth and at the correct speed.

TIA

 

Maybe cat conv. is bad? I had the cone inside get loose and turn, restricting flow. Might be letting some emmissions go by because of that too?

 

Several things come to mind with the idle and the 4.3. Check the intake manifold gasket for leaks and clean the EGR valve.

MikeyB

 

Idle air control motor via the ecm controls the idle. If you go adjusting it, it will never be right. It will move the tps to an unnacceptable range. like said above.......vacuum leak at intake or stuck egr, other vacuum hose leaks......another thing I've seen quite a few of, in regards to the slight miss, is the valve stem getting pulled up into the valve. Seems to be on younger drivers with a heavy right foot ,though! You can try to back off the rocker arm nut and see if it helps. If it does....get ready for a valve job.

 

94 is a combined year, they went from tbi to mpi injection, which one do you have? What is the dom?


Tim

 

Dosen't look like any TBI i've ever seen. but I don't see the 6 injectors for MPI either.

Attachment 22327

DOM- 8/93

BTW, there is a small vacuum leak under the dash for the climate control but that shouldn't cause a miss or low idle( I did say shouldn't .......)


Thanks for the replies.

 

that truck might be CPI "centralized port injection" when the main injector (central) starts going bad and leaking, it will cause the troubles you previously mentioned

 

CPI is correct, G.M. had lots of problems with the injector poppets clogging up with carbon, the easiest fix was to use Chevron Techron fuel injector cleaner, just pour it in the tank when adding some gas. I would recomend using 2 separate doses back to back before anything else along with a fuel filter change. That is the most common cause for a skip on that vehicle. The vacuum leak could have an effect on the idle so you should find the cause of the leak, it is probably a chaffed vacuum hose or a broken or cracked connection for the selector side of the climate control. let us know how you make out.


Tim

 

I had one of the CPI injector tubes get clogged once as well. It ook about a 250 mile trip with 4 cans of injector cleaner in the tank to clear it up! Customer was very happy that they didn't have to replace it. They aren't cheap. There miss was very prominent though, yours seems very light. Worth a shot though!

 

Thanks guys! I'll go get a few cans and start cleaning.