Rough Idle, misfire and high idling issues

[wlkstout]

My 1991 3.1L Olds Cutlass Supreme Coupe started running rough a few weeks ago.  Started out like maybe a dirty fuel injector.  Within 3 days it started to idle extremely high, 1700rpm's in gear and 2300-2500 in neutral or park.  It will hold these rpm's for a while, then drop harshly to 400-800 rpm's, will misfire and will sometimes then stall.  Sometimes it will not start and then you have to hold the throttle open a little.  At times you could turn it off and then back on quickly and it would run for a short period and be fine.  Today before I changed the air intake temp sensor, it would stall and not start unless I gave it some gas, and then I changed the sensor, idled fine for 15 minutes, took it out for a drive and about 1/4 mile down the road it began to idle high again.  Checked the fuel pressure and it was the same as below.  I have replaced the ecm temp sensor, air intake temp sensor, idle air control sensor, fuel filter(3 months ago).  Fuel pressure is 43-45psi with the key on and 38-40 at idle.  No fuel in the vacuum hose from the pressure regulator, nor any vacuum leaks that I have been able to find.  It will throw a code 35.  Not sure if it is the injectors or maybe ECM or ....  Looking for some insight into the Olds issues before I pull the rest of my hair out.  Thank you

 

I did notice the ECM was not original.

[Galaxie500XL]

Classic symptoms of a vacuum leak.  I'd look at the vacuum line going to the power brake booster first--a bad hose, or a vacuum leak.  Disconnect and plug the booster hose, and see if the problem improves.  Or, it could be because of where the hose sits, and it's tendency to get very hot, and get oil on it that you've got a hole in the hose itself.

 

 

 

 

 

CODE 35

Trouble Code 35 indicates a problem with the Idle Speed Control (ISC) circuit. It will be set when the closed throttle engine speed is 200 RPM above or below the desired (commanded) idle speed for 50 seconds. Possible causes include:

1) Vacuum Leak (High Idle) - Also check for binding of throttle blade or linkage.

2) System too lean (High Air/Fuel Ratio) - The idle speed may be too high or too low. Check for low regulated fuel pressure, water in the fuel, or a restricted injector.

3) System too rich (Low Air/Fuel Ratio) - The idle speed will be too low. May exhibit black smoke in exhaust. Check for high fuel pressure, leaking or sticking injector.

4) Foreign material in throttle body.

5) Faulty IAC Valve electrical connections.

6) Faulty PCV valve.

7) Faulty IAC.

8) Faulty ECM.

[wlkstout]

Galaxie500XL, thank you for your suggestions. 

 

I did check the booster hose today and it appears to be intact. I took it off and it has been replaced as it appears to be realitively new.  That being said I did purchase the Olds in April of this year, so I don't know all of her history.  Today it would not run again without some throttle assistance so I went over the ground wires, checked for electrical activity with my volt meter on the IAC, MAP, TPS, EGR connections- all seamed ok. Today it threw codes 33, 44, 45 and again 35. It did run better for a bit after I reconnected the booster hose, so I took it out and wasn't even 100 ft out of the driveway and the issues came back....rrrr.  Was really hoping I had missed something with the booster hose.  I have pulled the ECM fuse to reset the codes and the 35 has returned 3 times today but the others only once.  Granted they threw when it was idling on the low side and misfiring in the driveway. 

[rich_e777]

_{I`d replace the mentioned sensors if they show their age and run some injector cleaner through the system if no vacuum leaks were detected. Maybe run by a junkyard and get a TPS and IAC to see if anything changes when they are replaced. I know a weird TPS can do some funky things.}

[wlkstout]

I did the TPS sensor with no avail. Will be getting plenum gaskets and trying the injectors next. Thanks for your help.

[vipmiller803]

Remember that vacuum leaks can be anywhere before the intake valve. This includes lower intake manifold gaskets. Those are usually less likely than a crack in a vacuum line, but they do happen. I would check the lines by capping them then go from there. In a 91 vacuum was a little more used, like in cruise control and trans modulator, so everything needs to be checked, not just the brake booster.

[wlkstout]

Tonight while working on it I had something happen that had not happened before. I got a fair amount of moisture(coolant smelling) in the exhaust.... Checked the oil, coolant and nothing has combined all clear. Radiator wasn't bubbling.  So now I am thinking it is the intake manifold gasket...shoot.  I have not replaced that before on this engine, is it a fairly easy job? Can it be broken down and put back in a day?  Thanks

[wlkstout]

Ok, I pulled the intake and got it put back together yesterday with one huge problem.  It won't start.  I feels like it is fighting itself to start and the one time it did start but ran horrible was when I forgot to put the brake booster line back on it.  I had pulled the plenum to check the injector wiring harness and pulled it.  It appears to be dumping a large amount of fuel into the intake.  I pulled the plenum and fuel is running out of it.  I am leaning towards the pressure regulator but there is no fuel coming out of the vacuum line. 

 

Any help is greatly appreciated.

[Imp558]

Have you done plugs and wires? A couple years ago I had one that got coolant into the intake and saturated the plugs. Even blowing them dry didn't help, I replaced them and everything was fine. That was a 3800, but wet plugs are wet plugs.

As far as the search for vacuum leaks goes a propane torch (unlit,lol) makes for an easy way to find them. Also, there could be vacuum lines run as low as the drivers lower front fender at a vacuum bottle. I believe there should be one since it's a 4t60 with a vacuum modulator.

[wlkstout]

I did not replaced the plugs since replacing the intake.  But there were replaced 3k miles ago when I bought it.  Hopefully the didn't die as a result

[wlkstout]

Well I found out what was wrong and it was not good.  I had flipped an intake and exhaust pushrod, bending the exhaust rod which inturn bent an intake valve...smh. Now the question is do I want to fix it or scrap it... :-(

[will_s95]

that's rough man... maybe hop on craigslist and see if you cant find a new engine? 116k is worth that IMO

[wlkstout]

Well, luckily after pulling the heads and finding no damage to the pistons, I had the heads redone and she is back on the road.  Was extremely nervous when I first fired her up.  Now she purrs like a kitten. 

[wlkstout]

Now I was driving it today and the freaking thing started holding idle rpm's then dropping and sputtering again.  The only thing I did notice different was when I backed it in the driveway it had an foul smell to the exhaust, like catalytic converter egg smell.  Would a failing cat cause similar problems?  When I rebuilt the top of the motor I used felpro gaskets and torqued everything to specs....don't see how it could be the intake gasket again.  Any help is greatly appreciated.

 

It did throw a code 33. MAP sensor voltage was too high for 4.8 seconds when throttle angle was less than 2%.

[wlkstout]

I have an extra used map sensor and just swapped it out but it did not make any difference... so disappointed.  Help? Thanks

[Imp558]

Excessive back pressure from something like a converter can certainly affect the way the engine runs.

[wlkstout]

Put a vacuum gauge on it an it is pulling 18psi at idle and 22psi at 2500psi. No decline in pressure held strong.

Drove it for 2 days with no issues, then last night it did it again halfway home from work, it cleared up after about 3 miles and never returned for the 10 more miles home.

Was looking at it again and found a capped off vacuum line that goes to the ac/heat reserve tank under the car. Will be fixing that today.

[Taylor]

What spark plugs did you put in the car when you did them?  I know it might seem minor, but 60 degree engines are picky about what plugs they like.  If you put platinum of any kind, iridium, or anything bosch crap (especially the +2's or +4's), then I'll bet that is part of the problem.  The 3.1 mpfi engine is happiest with good ole AC Delco R44LTSM plugs.

 

The waste-spark DIS system on the 3.1 runs hotter than most platinum plugs can handle.  You get about 3-5K miles on them and it burns the platinum right out of them (especially if they are cheaply made, or you are running a higher than normal compression).

[wlkstout]

Ok. I did put autolite iridiums in it when i bought it. If that is the case I will swap them out.

 

I reconnected the vacuum line to the reservior tank and checked all of the rest of the vacuum lines with a vacuum pump and all are holding pressure. I did notice the pressure at idle was still at 18 psi but the 2500rpm pressure was now 21 psi.

 

Thanks for the plug tip

[wlkstout]

Ran until saturday without issues then idle stuck and then bang, idle drops and rough idling. Was able to get a vacuum gauge on it and it was down to 5-6 psi at idle. Snap the throttle and it would go up to 21psi then back down to 5-6 psi. Turned off and back on and runs normal, 18psi at idle runs smooth.

So I let the plugs go until it did it again and then changed them saturday after it acted up. We will see how it does. Hopefully it works.

Did notice the autolite iridiums were all gaped from .053-.057. I know they were not that far when i installed them believe they were at .045 like the ac delco's.

[wlkstout]

Ran fine until Thursday the 7th. Then the high idle stuck again. I changed the EGR valve(have a spare used one) and after doing the idle it would not idle properly in the driveway. Kept holding a high idle 1500-1800rpm. At first I thought it was the idle relearn but it was not and thru a code 35 for idling. So I did put a spare (used) idle control valve in it and so far so good. Hoping for the best.

 

As a side note it does run better with the plain old copper AC Delco spark plugs. :-)

[wlkstout]

Drove about 25 miles today and it acted up again. This time worse than ever. Usually clears up and will do it for once or twice and go away. But today it would not stop idling high 2500rpm and then rough 300-700rpm sporatic idling all the way home and then around town a couple times. Kicked another code 35. Checked the iac, tps, egr for shorts in wiring, ohms and voltage all seamed ok but i did change the tps out with a used one. Have a egr and iac ordered rockauto had a egr on closeout for $16, cant beat it. After i got it back together it did run normal. Ugh.

[wlkstout]

Mini update.

Did replace the idle air control and EGR with brand new ones. So far everything's working. Not sure which one it was but I think it might have been the tps. As the last time it was acting up, i disconnected each one one at a time and the only one that affected the high idle was the tps... so idk but thankfully it has been good.

[wlkstout]

I am going to look at the catalytic converter this spring as i think it is going bad. Get the egg smell everynow and then.

[Schurkey]

Schurkey's usual advice:  Connect a REAL scan tool, look at the data stream when it acts up.

 

You can replace parts all day long, but if there's a wiring problem or ECM problem, you won't fix anything.