1994 DOHC 6 Racing and then sputtering

[bluecalais79]

My brother just picked up my old Teal 1994 Cutlass Supreme from my Dad who has had it since 2012. Already my brother has had an issue with the motor and I can tell he's not to happy about it. Specifically, when dead cold, upon starting it the motor races to over 4000 rpms like its going to explode and then within 3 or 4 seconds it falls way down and sputters and nearly stalls out/runs very rough and then races way back up to high RPMS, and keeps repeating this until it's fully warmed up and then it smooths out. But, he's advising it's starting to now do this all the time regardless of the temperature of the motor, and just overall runs rough.

Does anyone out there have an idea what may be causing this? I will say my Dad hardly ever drove this car and it was always outside for the last 6 years. I'm speculating the car's fuel system has now been jostled by now being used everyday and the motor has a Fuel Pump/Fuel Filter/Injector issue(s). And the Service Engine Soon Light is occasionally going on as well

Has anyone had this issue with the Quad 6 motors?  Thanks.

 

[digitaloutsider]

Check the IAC and look for any vacuum leaks.

[bluecalais79]

Figured it out IAC. Idle Air Control Valve. I'm good with motors up to 1988, anything after that, not so much.

Much Appreciated! I think this is the malady.

 

 

Edited December 13, 2018 by bluecalais79

[Imp558]

2 hours ago, digitaloutsider said:

Check the IAC and look for any vacuum leaks.

Surging is almost always an IAC

[bluecalais79]

Just ordered one, NOS  AC Delco, thanks, man. I don't think that was ever replaced. Long overdue.

[Imp558]

A good cleaning may make it driveable until the replacement arrives.

[bluecalais79]

Thanks, he's on that. It's his baby now. 

[rich_e777]

"Quad Six" I kind of like that.

Almost been here a decade or... wait, nope been here a decade and have never heard that term before.

[bluecalais79]

That's what the sales reps were calling that motor back in 1994 when I bought this car new, it stuck with me all these years. I bought one of these IAC valves for my 3.1 as a back up. Lesson learned here for sure.

[digitaloutsider]

I've personally never heard it, or seen it documented in GM literature that way, but anything is possible. The only thing I ever saw GM refer to it as was Twin Dual Cam, 24 Valve V6, or DOHC.  The Fiero DOHC prototype simply had "DOHC 24 VALVE" stamped on the fuel injector cover.

Man it's a shame they never built that car.

[MemphisMan]

On 12/13/2018 at 8:07 AM, bluecalais79 said:

My brother just picked up my old Teal 1994 Cutlass Supreme from my Dad who has had it since 2012. Already my brother has had an issue with the motor and I can tell he's not to happy about it. Specifically, when dead cold, upon starting it the motor races to over 4000 rpms like its going to explode and then within 3 or 4 seconds it falls way down and sputters and nearly stalls out/runs very rough and then races way back up to high RPMS, and keeps repeating this until it's fully warmed up and then it smooths out. But, he's advising it's starting to now do this all the time regardless of the temperature of the motor, and just overall runs rough.

Does anyone out there have an idea what may be causing this? I will say my Dad hardly ever drove this car and it was always outside for the last 6 years. I'm speculating the car's fuel system has now been jostled by now being used everyday and the motor has a Fuel Pump/Fuel Filter/Injector issue(s). And the Service Engine Soon Light is occasionally going on as well

Has anyone had this issue with the Quad 6 motors?  Thanks.

 

If the IAC isn't the culprit, it could be the lower intake manifold gaskets.  My car was doing the same thing, but replacing the IAC didn't fix it.  Mine was leaking LIM gaskets.

[bluecalais79]

Thanks, that's a plan to look at that if the IAC is not working right or at all. I was the original owner of the car and I had it until 2012 and the IAC was never replaced. And in the 6 years my Dad owned it he never replaced anything.

[bluecalais79]

Ok, on to the next issue. My brother installed the new IAC valve and it fixed the low idle sputtering, all is well there. But he's advising it's idling in park or neutral WAY TO HIGH but once he puts it in gear it's fine, it settles right down to where it should. I myself have never adjusted the idle on these cars, I wouldn't know where to start. Is there some part on the motor where the park/neutral idle can be adjusted so it doesn't race?   Thanks All, much appreciated. We get this last bug out off it and I think we're good to go.

[MemphisMan]

When it warms up, does it idle correctly in neutral? If so, LIM gaskets are leaking.


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[Imp558]

Also check the TPS:

Slide a pin alongside the blue wire past the seal until it touches the pin inside.

Turn the ignition on and read the voltage at the blue wire (hence the pin) as you move the throttle. 

Should see almost 0V on one end up to almost 5V on the other.

Memphisman is of course correct that a vacuum leak can cause this but it seems fishy that it was idling low before so make sure all the vacuum lines are good, especially ones that may have been jostled during the IACV install.

[bluecalais79]

Thanks, will do, I think it's time for a road trip to NJ to help him figure this out

[bluecalais79]

Ok, back from the road trip. Problem solved. Turns out the IAC I sent him directly on E-Bay was a total piece of S*&T. Luckily I ordered a 2nd one from my local parts store and doubly luckily I actually went and picked it up last week. I pulled the one I bought my brother and it literally fell to pieces in my hand. What a rip off. I installed the 2nd one I brought with me and the car is now running as it should, no racing, no sputtering, all good.

Mission accomplished. Thanks everyone for this tip, it took some additional effort but it's now right.