Buick high idle speed at start

[HEMI-V8]

Hello.

 

Is it normal that my Buick is idling so long on these speed ?

 

cold engine - room temperature 70 °F

 

it may needs around 3-5 minutes till it revs around idling around 650 rpm

 

[video=youtube;8JS_6ortl0U]https://www.youtube.com/watch?v=8JS_6ortl0U

 

Thank you.

[Nas Escobar]

It's fairly normal to idle at 1000 at first then go down to 650-700 rpm but if it worries you then you can start checking for vacuum leaks. Usually a vacuum leak will cause the engine to idle higher than normal.

[HEMI-V8]

could it also be the IAC valve ?

 

vacuum leaks are horrible to find

[RobertISaar]

normal GM programming. i can't remember if you have a 3.8 or 2.8/3.1 car, but this is the commanded idle speed table from a 90 regal with a 3800.

 

 

on the left is commanded speed while in drive, on the right is while in park/neutral. the 2.8/3.1 table is similar.

[HEMI-V8]

Thank you - I got the 3.1

[Michael Savage]

Now if you're idling at start above those values IDE check you IAC I've got one in my console for shits and giggles I bought it from pull a part and apparently it's messed up. It idles at 2800-3400rpm and as soon as you put it in drive and take your foot off the brake the cars takes off. I thought it was funny, and possibly cool if you're gonna race someone you get a head start. I've been meaning to take a video of that IAC but I don't mess with it very often. As far as driving with that IAC it drives good but I didn't drive it but a mile or 2 because I didn't trust that IAC for in town because I didn't wanna smash into someone.

[HEMI-V8]

Okay, good to know.

 

Today I´ve seen that my air intake hose ist on the throttle body side broken. Could that be a possible error source ?

[RobertISaar]

unless you're running an 88 car with the MAF still enabled(i don't know how well recalls get done overseas for something like this), the only thing that will do is allow unfiltered air into the engine, which isn't a good thing, but it wouldn't effect drivability.

[Michael Savage]

IDE honestly pick up a IAC from a scrap/junk/part yard and try that. 5 minute high idle sounds like an IAC, either that or take it off and see if it's really dirty if it is that could be causing it to stick if it's got carbon/oil mixed build up on it. Can of Carb Cleaner spray it clean and wipe it down with a grease rag then spray it again and let it dry then see if that helps.

[HEMI-V8]

So the IAC and the whole throttle body are still really clean. I have noticed that the engine is also running in idle a little bit rough. spark plugs and wires are relatively new.

Could it also be the intake temperature sensor ?

Edited July 26, 2014 by HEMI-V8

[Nas Escobar]

Running rough may be coil packs.

[HEMI-V8]

is it possible to test the coils ?

[Nas Escobar]

If you pull the spark plug cables from the coil pack, you should see the spark. The faster the spark with the boot off, the better it is, or in other words less spark means the coil pack is failing.

 

I think there's a safer method than this but I've been told this is one way. Whether it's right or wrong is another thing.

[Michael Savage]

Intake Temp Sensor could be bad, they're about .50 to $5 at part yards.

But I agree with checking your coil packs, you might get shocked, but 25,000 volts jumping to you isn't as bad as your engine going bad. Also the shock isn't that bad from the coils, scares you more than anything the first few times.

[HEMI-V8]

UPDATE: I was today at my buddy´s auto shop and he tested my Regal with his "new" (used) Tech2.

 

Then he saw that the Intake Temp Sensor is O.K but the vacuum is not as it should be.

 

He said the rough running and to high idle is a symptone of an vaccum leak.

 

Now I will install a new intake manifold gasket and checking the vacuum hoses.

 

 

Is there such a thing like an vaccum chart for my Buick anywhere ?

[RobertISaar]

Is there such a thing like an vaccum chart for my Buick anywhere ?

 

a diagram for the different vacuum lines?

 

i'll need a year/engine/transmission to pull an accurate diagram for your car.

[HEMI-V8]

Yes, such a diagram would be very useful for me i think.

 

1990 Buick Regal Limited

3.1 MFI V6 LH0 (engine code T)

4T60 4-speed automatic transmission

VIN:2GE WD 14T 9L141 3855

[RobertISaar]

this looks like the best i can pull through alldata. i might be able to dig up something more detailed if you need more on a specific system.

 

 

i did notice it doesn't show the line for the transmission's vacuum modulator, that would show up on its own vacuum port about 2 inches to the left of the throttle.

[Michael Savage]

Sure fire way to test where you're leaking. But a spray bottle fill it with water. Start the engine and squirt water on the hoses and around the intake ports and where the throttle body connects to the intake. If it stutters after you squirt that's where the leak is. Helped me figure out my EGR adapter was loose. Be careful not to spray electrical connections, they have a water proof seal, but best not to chance it.

[HEMI-V8]

Alright, till now I checked vacuum leaks always with brake cleaner, but of course water could be better because the effects are stronger than with brake cleaner.

 

UPDATE: Ive notices no differnce on engine running when Im spaying water / brake cleaner on the vacuum lines and the manifold.

 

But I have seen that no reaction will be when I am disconnect the IAC valve when the engine is running cold ! - is this normal ?

Edited July 28, 2014 by HEMI-V8

[Garrett Powered]

you can monitor the IAC activity and tell if it is letting enough air in.

[RobertISaar]

But I have seen that no reaction will be when I am disconnect the IAC valve when the engine is running cold ! - is this normal ?

 

possibly normal.

 

the IAC is a stepper motor, when you unplug it, it stays in the position it was last commanded.

 

as the engine warms up, less air through the IAC is needed, so it starts closing. if unplugged during this, more air than expected will be going into the engine, which would normally cause idle speed to go up. GM implimented a secondary idle speed control scheme that advances/retards the spark advance to keep the engine near the target speed(it's actually the primary control mechanism since it operates without delays, but there are limitations).

 

 

so, unplug the IAC while the engine is cold and as it warms, the ECM will command less advance to combat the higher airflow. if it runs into a retard limit, then it won't be able to compensate enough to keep it at the target speed.

[HEMI-V8]

Good to know. Thank you. I will report when I got some news after installing the new manifold gasket.

 

Additional question: Should I change only the plenum gasket (no.88) or also the gasket of the lower manifold ? (No. 26)

 

Edited July 28, 2014 by HEMI-V8

[HEMI-V8]

Any answer for me ?

[RobertISaar]

i didn't see the edit.

 

generally, the 2.8/3.1 lower intake gaskets don't require replacement, they'll last the life of the engine. the later 3100/3400 engines did have issues with the lower intake gaskets.

 

i would say that unless you see some kind of indication that it is at fault to leave it.