Rough idle, stalling

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1991 Chevrolet K1500 4.3 V6, running rough at idle and vehicle stalls. Thought it was the negative battery cable, replaced that. Fuel filter looks ancient, will replace it tomorrow. Would a plugged fuel filter cause "Service Engine Soon" light to come on? It came on briefly this evening. If it only came on briefly, would it store a code? Based on what I've read, i'm leaning towards EGR valve stuck open (?). Your thoughts/sugesstiins?
 
I suggest you see the plugs. Got some corrosion on top cap of them, on my car it made rough idle, stalling and misfiring, w/o check engine light.
 
Also check cap and rotor. Remove and clean the TBI. Hope you find the culprit and it's n easy fix
 
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Something that old needs a good going through at this point

Plugs, wires, cap and rotor

Air/fuel filter

PCV valve

You can even get Genuine ACDelco versions of all these things for next to nothing on RockAuto

Is it a QJet, or Throttle Body Injection?
 
Air filter and pcv were changed when I purchased the vehicle a year ago. Plugs, wires, rotor and cap were changed about 13k miles ago (which was a out 7 years ago). I changed the fuel filter this morning. It seems to have fixed the problem. Will give it a few days to see.
 
Ok, running better, but still rough idle. Wants to stall, then revs back up. I will chk plugs and throttle body. Would i be able to see EGR move from the outside?
 
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Last fill up, i ran a fuel system cleaner. So, i was good, so i thought. Changed the fuel filter and that seemed to help slightly. This evening, i poured a bottle of Gumout All in One with Regane and put in fresh, non-ethanol top-tier fuel (Shell). Vehicle seems to be idling smoothly and not stalling out.
 
The vehicle was continuing to stall more frequently. A friend suggested it was the Idle Air Control Valve. After reading about Faulty IAC symptoms, this sounded like a proper diagnosis. He has a 91 S10 with the same engine.

I had already purchased new plugs and replaced them this morning. The number 1 & 2 plugs were loose. After replacing the plugs, the vehicle started to stall at idle. But after running it for a while, things improved. I have driven it all day without it stalling. Idling stills seems a little rough, but not enough to stall.

Wondering if the IAC could be faulty. At $55, I dont want to replace it if I dont need to. I will drive it for a few days and see how she fares.
 
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Plugs or vacuum leaks come to mind. Fuel filters will starve the engine generally at high speeds when the demand for fuel is there. I had one make my top speed at 55 mph and shuddering. The engine will barely run if the EGR is stuck open. Check for codes.
 
Different year, different engine, but your problems are very similar to what I just went through. Cherry pick this reply for any possibilities.

The idle on my Escalade was driving me crazy. Sometimes good, sometimes bad. Sometimes rough when the AC was going, sometimes at start up it was close to stalling. Other times it was just plain rough. Did all the basics.. fuel cleaners, plugs, wires, etc. Then I started doing more expensive things like a new throttle body to rule out the TPS and IAC. It was better, more stable but still shaking a bit.

Then I got a check engine light for a knock sensor. The replacement includes a new intake manifold gasket. I did it myself and noticed how degraded the intake manifold gasket was. I put it back together and instantly noticed the difference. No more shaking no more rough idle. And Ticking noises were gone too. So it was one of the two that solved my problems. And for now on replacing the intake manifold gasket will be one of the first things I do. Because if you do it yourself it's not that expensive
 
Originally Posted By: otis24
Ok, running better, but still rough idle. Wants to stall, then revs back up. I will chk plugs and throttle body. Would i be able to see EGR move from the outside?


You should be able to reach under the EGR valve and move the diaphragm to see if it's moving smoothly. I had a Saturn that started idling rough and feeling like it was going to die between gears (manual trans). When I checked the EGR as above, I felt the mechanism hanging up. A year-old replacement valve had corroded so it was sticking open just barely.

There's also an EGR solenoid that you can check for vacuum. It should keep the valve closed at idle. With the engine runnning, you can open the throttle and feel whether the EGR opens.

I would check for codes using the paper clip method linked above, and also clean the throttle body before spending money on parts. Find out where the bypass passage for the IAC is, so you can clean that.

When you replaced plugs and wires, did you pull the cap to check/clean the contacts inside? Vacuum hoses would be another maintenance item to go through considering the vehicle's age.
 
These old TBI units have issues, they are quick and easy to rebuild, the difference it makes is amazing.

For $54 ea I would swap the TB injectors with STANDARD MOTOR PRODUCTS TJ1 from Rock.
I would also get a TB repair kit also it cost $33 inc gaskets and regulator, STANDARD MOTOR PRODUCTS 1702
 
Replaced the IAC Valve. That wasnt the problem. While driving through the carwash with undercarriage wash, the vehicle almost stalled. Fortunately, the SES light came on temporarily. The mechanic at work put his scanner on it. Got a code 33 for MAP sensor. Thankfully I did not replace the EGR valve. The MAP sensor was within specs and "barometer" limits (whatever that means). Bottom line is, probable vacuum leak. I havent priced a MAP sensor yet. If I cant find the leak, I may relace the stiff plastic vac lines with rubber vaccuum hose. There's not too many and shouldnt cost too much. Need to check all the ports on the TBI where the vac hoses hook up and make sure they arent plugged.
 
Just replaced the MAP sensor. It seems to be the fix. Won't know for sure till morning. It seems more persnickety in the mornings when it starts up from a cold start.
 
The old GM TBI systems were notorious for the gasket between the TBI and intake to develop leaks. An easy way to diagnose is when it is acting up, spray small amounts of carb cleaner around the gasket area and listed for the RPMs to rise. Dead giveaway of a gasket leak. I saw many of them back when I was a service station jockey in high school in the early 90's.
 
Replaced the TBI gasket. Cannot detect any vacuum leaks. The only thing left I think it can be is intake gaskets. Going to have to bite the bullet and replace them.
 
Replaced the fuel pump. Back to running like a champ. Part of me woners if the use of TCW3 shortened the life of the fuel pump or if the pumps number was just up. About 93k miles.
 
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