I got a 1989 s10 with the 4.3 it has a rough idle at low acts likes it's about to die. Then at times has high idle. But for the most part it's the low idle. I have changed out the O2 sensor. The tps and coolant temp sensor. Check engine light was on and the code was for the o2 and tps but changed both out and nothing changed butt that's when I started getting high idel after I changed out the o2 before that it was alway low. What else could be wrong with it or what could I check.

 

IAC idle air control valve?

 

I changed it out today and same thing just now well kinda now it revs up when sitting at drive and foot on the break. And still at times drops on it face and bout stalls out. But it did help some what and new pcv too

 

Electrial connectors is the next that comes to mind. Seems it is loosing the signal intermittently.

Next thing also is to check on the temperature sensor.

Ignition timing? Just to make sure as this is also the TACH signal for rpm for the ECU.

I would start looking and where possible measuring the electrical wiring.
Also make sure the engine ground connection and ground connection on the firewall behind the distributor are o.k. (no corrosion, not loose, cables are looking good [copper wire is not black] and check all sensor couplings for that as well).

 

I changed out the temp sensor last weekend. Will check timing and connections today. Thank you for the help

 

Ok so checked all the connections and all where good. Checked behind the cap and was good no green or anything like a bad wire would look like. It does idel better but still at times I can be at a red light holding my breaks and it wants to jump then falls back down

 

Down to all the vacuum lines maybe.

Had that on mine. The rubber knee which attaches to the TBI was rotten. Sometimes but just sometimes it could pull air from there.

 

Ok so checked all the lines and all are good but today my check engine light came on and it was the tps but I just put one on it about last month it says low volt what or how do I check it

 

Rough idle just started,been great after tune up,came back from trip low on fuel an thats when surge started in neutral an drive,almost stalling..could it be bad gas at bottom of tank..thanks .

 

Running out of options here.

Another possible guess: Go look for the bonding straps. They have to be in good conditions and in place else they can generate all kind of errors.

Would need to measure resistance of TPS - and/or voltage of the various sensors to see if you have an intermittent. Difficult on a distance to tell.

Have a close look at the ECU under the dash on passenger side. Especially the connectors.

IN ALL CASES WHEN DEALING WITH THE ECU REMOVE THE BATTERY CONNECTIONS AT LEAST 10 MIN. BEFORE UNPLUGGING.

I would start to suspect a corroded connection somewhere giving wrong values.