Rough Idle

[steamer482]

Here’s the deal gang,

My 97 Jimmy was having a rough idle recently, (about two weeks now). It would only really act of when the car was in drive, but at a complete stop, or in park. When in park it is not as rough, but as I said, when in drive and stopped bad, Sometimes it feels like the car will stall, but I have not reached this yet. I spoke with a few friends and they said to check the ERG valve, since when the car is first started it runs fine, but after about 5 minutes, it runs rough. I replaced the valve and it still runs rough, but not as bad. I am guessing maybe next to change the fuel filter and spark plugs, but I think it may be a bad sensor somewhere, but no check engine light. I adjusted the idle at I am at about 600 rpm. Any ideas, anyone!!!

Thanks

Steamer

[BOOZER]

The EGR system is a common problem on this engine, but its not always valve at fault. The EGR port in the lower intake has a tendency to flake off
carbon buildup that gets stuck in the pintle of the valve. People replace the valve, it cures the problem for a while. Most of the time you can remove the valve & clean it & the port with a round wire brush, & start the engine to clear the port. I beleave there is also a reflash of the PCM that will
purge the valve at startup. Also "GMMERLIN" mentioned that TOMCO makes a screned EGR gasket
witch is something I did'nt know.
Last I recomend using a fuel detergent once or twice a year, eather the GM product or "TECHRON"
that you can get at most parts stores.
By the way the screw on the T/B isnt there to adjust idle speed, thats what the I.A.C. valve does controled by the PCM. It's not adjustable!

[steamer482]

Thanks for the reply Boozer,

I am however this weekend replacing my spark plugs and fuel filter, hopefully this will solve the problem and make the engine idle smoother.

Thanks again,

Steamer

[GMMerlin]

I don't see many 97 model trucks with EGR problems like the older models had.
Rough idle concerns on those models I start to lean towards the possibility of a sticking poppet or leaking fuel pressure regulator (after ruling out vacum concerns, schewed sensor readings and misfires)
Also adjusting the idle is a NO-NO....that is controlled by the PCM and reads TPS position to command idle speed.
Low idle concerns and sticking throttle bodys, I start with cleaning the throttle bore and blade. Really bad ones I may adjust the throttle blade to add about.02 volts to the tps reading.

[steamer482]

Originally Posted by GMMerlin

I don't see many 97 model trucks with EGR problems like the older models had.
Rough idle concerns on those models I start to lean towards the possibility of a sticking poppet or leaking fuel pressure regulator (after ruling out vacum concerns, schewed sensor readings and misfires)
Also adjusting the idle is a NO-NO....that is controlled by the PCM and reads TPS position to command idle speed.
Low idle concerns and sticking throttle bodys, I start with cleaning the throttle bore and blade. Really bad ones I may adjust the throttle blade to add about.02 volts to the tps reading.

Hey GM,

Steamer here.

I bought my 1997 Jimmy used last year. When I bought it, it had about 69,000 on it. Now I am at around 87,000. A few weeks ago I noticed the rough idle, around the change in weather and temperature. What was happening is the truck would start fine, hardly and rough running or idle. After about 5 or time minutes of running, the engine would run rough only when I came to a stop and in drive. It was beginning to get so bad that it felt like the engine could stall but did not. I spoke with some friends who think they know cars and suggested change the EGR valve. I removed the old one and did not note much carbon buildup, installed the newer valve and the engine continued to run rough but not as bad. A few recommendations from friends was to check the distributor cap, which I did and looks good, but the spark plugs probably have not been changed since the truck was made. Another concern with to possibly replace the fuel filter, but I really don’t have any lack of pickup and speed. I am planning on changing to spark plugs this week end, but looking at the wonderful Vortex engine set up, the plugs, as you know, are buried deep on each side of the motor. It appears to only way to really access them is to pull each tire off to access them, ANY IDEAS??? Call me crazy, but I do want to resolve this issue quickly and not have to spend a crap load of money either. The ERG valve was not cheap, some hopefully spark plugs and a new fuel filter could correct the issue. Also, it has been about a week now since I installed the newer ERG valve and the idle seems to be getting better, but not by much. I was a little confused as to what the PCM , TPS, and poppet are. I know the basics of cars and that’s about it. Any more helpful ideas you can give me would be greatly appreciated. Again Thank you.

Frank

[mjohn]

Dear Frank...I seem to have the same problem you started with 1993 Jimmy 4.3 It starts hard and runs fine until left at an idle...then it loads up and stinks like gun powder...One year ago similar problem and mechanic said erg valve needed cleaning. We are entering winter here and it needs to work everyday..I ran 2 cans of Seaform through it with a tank of gas and that seemed to help some...MJohn

[mjohn]

Dear Frank...I seem to have the same problem you stated with 1993 Jimmy 4.3 It starts hard and runs fine until left at an idle...then it loads up and stinks like gun powder...One year ago similar problem and mechanic said erg valve needed cleaning. We are entering winter here and it needs to work everyday..I ran 2 cans of Seaform through it with a tank of gas and that seemed to help some...MJohn