Impossible to find vacuum Leak gm 3.1/High idle

[Dehaka]

All done at licensed shop:

New Headgaskets
New Intake gaskets
New upper and lower intake manifolds
Throttle body cleaned plate not sticking
New idle air control valve
New temp sensor
New thermostat
New throttle position sensor
Computer reprpgramed
New air filter
All fluids changed/flushed
Fuel filter
Smoke test shows no smoke
Pressure test shows it holds.vacuum
MAF swapped
New dash instrument cluster
Throttle cables not catching on anything.

Car takes off up to 30 mph without touching accelerator. Needed smog test in March but have been waiting to fix this issue as it wont pass like this. At wits my end. Car runs like a champ 95 k on the clock. Family Owned since new. Meticulously maintianed. Already 4 grand deep into a 2k car.....too late to go back and scrap it now. Mechanic who did the work cant find problem is "taking a step back/break for a week to come back to job from new angle" .

Open to suggestions. Last issue to fix and then this 6 month headache will be over.

All replies and opinions appreciated.

 

[bullwinkle]

Any chance of a power brake booster leaking? Must be a huge leak.

 

[Dehaka]

Any chance of a power brake booster leaking? Must be a huge leak.

Didnt think of that. Wouldn't it normally hiss? Brakes work good. Lol put new brakes too.

 

[Dehaka]

Forgot to add. Not light or codes.

 

[Trav]

I usually start by pinching off each vacuum hose one at a time to see if any make a difference. What are the fuel trims?

 

[Dehaka]

I usually start by pinching off each vacuum hose one at a time to see if any make a difference. What are the fuel trims?

That I'm not sure of. I will ask when he opens tomorrow.

 

[Soft Cars]

Was the high idle there before replacing the throttle position sensor?

 

[LazyDog]

You need to find some one w/ a good scanner and check Live Data Parameters.

 

[mk378]

As someone said in your other thread about this same problem (please don't do that), installing the TPS improperly can prevent the throttle plate from closing fully. Take off the big hose from the air cleaner side and confirm the throttle plate is against the side of the throttle body when no one is pressing the gas.

 

[eljefino]

What year is this bad larry?

If it's speed density (no MAF) take the air intake tube off so you can see the throttle body, and put your thumb over the idle air bypass hole when it's running. If that cuts the speed then the ECM wants it that high, for stupid reasons. Edit, I see it's a MAF, what the heck, try the test anyway.

Does it have an EGR valve? Those can be a vacuum leak but they usually sound "cammy" at idle.

 

[Luftmasse]

Can you post up the live data?

 

[Dehaka]

Was the high idle there before replacing the throttle position sensor?

Yes. It was replaced to see if that fixed the issue.

 

[dbias]

Recheck the idle air control valve. High idle but otherwise smooth running indicates that it is either stuck open or more open than it should be.

 

[clinebarger]

It's been awhile since I worked on a 3.1L....But there should be a IAC bypass hole in the Throttle Body, There shouldn't be much of any vacuum at the port if the IAC is fully closed (Zero Counts).

 

[DuckRyder]

what's it in? i recall early 2.8/3.1 having a fairly complicated base idle learn procedure...

 

[WobblyElvis]

Try this.....PCV tubing grommet into the upper intake, the one below the throttle cable bracket.

 

[Soft Cars]

Yes. It was replaced to see if that fixed the issue.

The reason why I ask is because if the throttle position sensor is not installed correctly, it will hold the throttle plate partially open.

 

[chemman]

Some vehicles with the 3.1 V6 engine have a nylon vacuum line that is located behind the alternator and is then routed in a very round about manner into the passenger compartment and is used by the HVAC controller to control various HVAC actuators. Check the vacuum line to make sure it has not been chewed on by a rodent, broken, etc.

A rodent chewed a nice hole into the one on our 1999 Buick Century a few years back. Hole was located close to the alternator body and was a pain to find.

 

[FishFry]

Best way to find a vacuum leak is with a propane torch.

 

[PF52]

+2 on the IAC concerns.

Have you tried taking it out for a test drive? Maybe the IAC doesn't "re-set" itself until it reaches a predetermined speed.