3.8 Initial High Idle

[averagewhiteboy]

Hey guys,

My Grand Prix has the 231 Buick motor. '85. I have a "problem" it where the engine will high rev when you first turn it on. I have no tach so I don't know exactly where it's at. I wouldn't say quite at 2,000... But probably close. Even when the engine is warm it'll sometimes do it. Often though, when I first turn the car on, it'll run a smooth, low idle. Then when I tap the gas to rev it, that's when it steps the idle up higher. The only way to get it to back off is to either drop the car into gear, or to let it sit for a minute. Then it just backs off by it's self. The funny part is, that the car idles so loud when it's at it's high idle (no mufler) that when it drops to a normal idle, it sounds like the car stalled out and died. haha! Hopefully it's something that can be fixed easily...

So, what could it be???

 

[383Camino]

I have no idea what does this, but my '91 S10 with a 2.8 does the same thing. Its a stick, so it makes taking off real easy as the engine is already going 2000rpm.

 

[averagewhiteboy]

lol. Yeah. A 2000 normal rev for my Honda would've been nuts. haha!

But my 89 Cadillac did the same thing. I was told it was the Idle Control something-or-rather. I forget exactly. But it was like a 15 dollar part. It basically just tells the engine when to stop high idling. So when it went bad, it'd just keep going until it finally reprogrammed it's self. It may be the same thing?

 

[SBCregal]

choke?

 

[85 Cutlass Brougham]

Your choke coil is out of adjustment. If the carb has never been rebuilt, the coil is likely pop riveted to the housing, and in order to adjust it you will need to drill out the rivets and install screws. The other possibility is that the fast idle cam has broken wherever it has it's limiter cast into it thus allowing the cam to go to high idle at the wrong time and not be pulled in by the choke coil and gravity. I had that happen on a Carter YFA 1 bbl on an AMC L6 once and it was a PITA until I changed it.

As far as the 1991 S10's 60 degree V6, it has fuel injection and the repairs I outlined here would not apply. It may be a sticking IAC solenoid ( Idle Air Control) or even a vacuum leak causing the high idle. The again, it could be something as simple as a binding throttle cable or broken throttle body return spring.It likely would not be a out of adjustment TPS as GM went to a auto adjustting system for it's TPS on many models sometime in the late 80's or early 90's and as such it would automatically compensate at each fresh start. A Final possibility is a bad CTS ( Cooland Temp Sensor). If this is bad, the computer never senses the engine has warmed up and may be improperly throwing it into high idle. If this is bad, your fuel economy would suffer as well since it puts the computer in a permanent open loop mode. Sorry I am not of much help, but I am better with imports when it comes to specifics on late models.

 

[383Camino]

Wow man thanks for the ideas. I'm at school so I have no place to work on it, but someday I'l get home and take a peek.

 

[averagewhiteboy]

Yeah man, that IAC was what went bad on my Cadillac. It was the 4.5L V8 fuel injection.

I mean, I'm not super worried about it really. Simply because I intend on putting a new engine in before summer anyway. But if it was something real easy I'd do it just for the hell of it. But certainly thanks for the great information guys!

8)

 

[85 Cutlass Brougham]

Oh, I fogot to mention one other possibility: a Worn out baseplate causing excessive play in the throttlesaft. this can cause it to step around the proper idle setting and put it on the fast idle side of the idle cam.

 

[averagewhiteboy]

^

Would that have anything to do with gear slippage at all? I wouldn't think so at least. It's just that when the car goes into the 2nd gear that it seems to high rev atlot at first, then it backs off. I don't know if the gear is slipping real bad, or if the problem is alot more basic...

 

[85 Cutlass Brougham]

^

Would that have anything to do with gear slippage at all? I wouldn't think so at least. It's just that when the car goes into the 2nd gear that it seems to high rev atlot at first, then it backs off. I don't know if the gear is slipping real bad, or if the problem is alot more basic...

That could be an out of adjustment TV cable, a bad transmission, or low fluid level.