Question about 1998 GMC Sonoma

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What should this truck pull as vacuum at idle

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17-21 inches of vacuum

Posted on Oct 08, 2009


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2005 Jeep 2.4 L rough idle

Vacuum leak. If your jeep has an ECG valve from the exhaust to the intake manifold you could be pulling an vacuum leak. Get a small propane torch and open the valve moving it around the engine compartment as you listen to the idle. When it accelerates and revs a little higher, you have found your vacuum leak.

Nov 21, 2013 | Cars & Trucks

1 Answer

My idle rises and falls in a steady pattern in my 1990 Geo tracker

Hi Connor,
It sounds like you have a vacuum leak somewhere and the pcm (power-train control module) is trying to compensate, you may also hear a hissing noise when the idle fluctuates, that would be a vacuum leak. If your check engine light is on, have the code pulled and it may point you in the right direction.

Mar 05, 2013 | Cars & Trucks

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The idle is sticking on park

High idle speed is usually caused by a sticking idle air control valve or a vac leak. The computer controls idle speed by how much air is allowed into the intake manifold.
is the check engine light on ?

Aug 26, 2012 | 1997 Chevrolet Tahoe

2 Answers

Having vacuum problems

check the vacuum line that goes to the fuel pressure regulator,pull the vacuum line off ,if there is fuel in the line ,the regulator has ruptured.

Jan 01, 2012 | Ford Cars & Trucks

1 Answer

What is the correct idle RPM for Durango 1998 5.2 L

Doing the opposite of what it should. Don't know, but the idle should be awful close to 800 on a warmed engine. You may have a vacuum leak causing your high idle. Check all your vacuum hoses for condition and proper routing. Pull one hose off and create a vacuum leak. It should cause your idle to raise. If it doesn't change the idle, there may already be a vacuum leak. By spraying carburetor cleaner around suspect areas, you can also find vac. leaks. The spray will be sucked into engine and change the rpm's.
Other possible causes might be a sensor ( CTS?TPS?) or an idle control valve, or some other computer controlled part.

Nov 20, 2011 | Cars & Trucks

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I have an 83 f-150 351w, in cold temps the truck won't idle till it warms up, then when it does it idles really fast, it also revs high, what can the problem be, also wen going at highway speeds after...

It sounds like it is working backwards. Around the time your truck was made the industry had different emissions standards for trucks and cars. There were less controls on trucks.

There were vacuum controls that would increase idle speed when the engine was cold. The way this was done is through a water temperature sensor that is commonly called a vacuum tree. It is called a tree because it is shaped like a tree trunk with a few branches and each branch has a vacuum hose. As water temperature increases the vacuum routing changes. The cold setting makes an idle step-up dash-pot raise RPM and close the choke plate. As the water warms, the internal parts of the vacuum tree move and change the vacuum ports.

When the ports change, RPM drops and the choke plate opens and low idle speeds are restored. With the choke plate open high speed operation of the motor is assured without bogging down.

I would say most of what can be wrong is cheap to fix. A new thermostat, perhaps a new vacuum tree. Your problem can also be the vacuum lines are not connected to the correct ports. One thing many people do is to adjust the idle speed at the wrong time. The step-up cams are not in the proper position and when stuff starts working everything is out of adjustment because the changes were made at the wrong time.

This is a job for an old school mechanic.

Oct 06, 2017 | 1983 Ford F150

1 Answer

Have a 99 Saturn, rough idles, stalls, high RPMs when first started, then idles to rough idle, what is the first thing I check?

Sounds like the EGR is hanging open causing an internal vacuum leak.... Check all vacuum lines first for cracks / splits and then pull the EGR and make sure the pintle is not stuck open with a chunk of carbon.

Oct 15, 2010 | 1999 Saturn SL

2 Answers

94 dodge truck 1500 2w/d

You could have either a vacuum line leak or an intake gasket leak. Often an intake gasket leak will also cause an oil consumption issue as the actual vacuum leak is at the bottom side of the intake and will result in not ony a misfire at idle but will pull engine oil into the intake causing a loss of engine oil. The other primary sources of leaks I find are broken plastic vacuum lines, usually on the passenger or rear side of the engine. The throttle plates on these do cause a loud hissing noise [normal] so it's often hard to pinpoint an actual vacuum leak unless the air cleaner is on which mutes some of the normal air noise.

Jun 08, 2010 | 2007 Dodge Ram 1500 Quad Cab Sport

1 Answer

A mechanic pull all my vacuum lines on my 95 dodge

Take it back to the mechanic and have finish the job he started.

Feb 23, 2010 | 1995 Dodge Caravan

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