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| High idle problem, unable to solve. (Page 1/4) |
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ketstang
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JUL 07, 08:27 PM
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I have read all the threads on high idle here and tried all the fixes and still can't get the car to idle below 1500 rpm. I mean I must have printed out a dozen threads and tried all their tests and possible fixes.
History: Car sat for 12+ years with old gas, gas tank was rusted out. That is when I got possession of it.
Work done - I put in a brand-new gas tank, sending unit, fuel pump and filter, all new rubber and metal lines from fuel tank to fuel rail. Fuel rail was taken off and cleaned, new injectors and fuel pressure regulator. All O-rings and gaskets on upper plenum were replaced with new. New TPS and IAC installed. New air filter.
I can cover the IAC port inside the intake area of the throttle body and the car idle will drop down to 800 and sometimes it will die, sometimes not.
I removed the IAC valve, and I can get the idle to drop down.
We have tried the propane hose test, carb cleaner test and Monday we did the cigar smoke test. Can't find any leaks.
Today I did the Pepsi can between the EGR tube and bottom of the upper intake thing and it is still is idling high.
It starts fine and idles rough around 1000 rpm for a few minutes. Then the idle starts fluctuating between 1000 and 1500 rpm, eventually the idle rises above 2000rpm.
I am at a loss on what to try next. I'm hesitant to dump any more money into the repair because it's not my car and the owner has spent a ton of money on all these new parts already.
Could the problem be the ECM and is there a way to test the ECM?
I have a new IAC valve installed. Is there a way to make sure it is getting power? I read in one of the posts that a guy wasn't getting power to his IAC (problem at connector), but he didn't post details about what the fix was.[This message has been edited by ketstang (edited 07-07-2023).]
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theogre
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JUL 07, 08:36 PM
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ketstang
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JUL 07, 08:42 PM
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I have disconnected the battery for a couple minutes and then drove the car about ten miles with speeds up to 50 mph. When I get back home and put it in neutral the idle speed is 2000-2500rpm.
I will look at the link you posted for more ideas.
Thanks for replying.
Kevin
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A_Lonely_Potato
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JUL 07, 10:49 PM
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you can check that the IAC is functioning by setting key to ON with diagnostic mode pins jumpered. the IAC will audibly be etiher extending or retracting(i cant remember which.) shut off, pull out the IAC after ~30 seconds of this. then if the IAC pintle is extended, push it back in. repeat, and if it is extended the second time, you'll know its moving.
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Patrick
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JUL 07, 11:08 PM
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| quote | Originally posted by ketstang:
I can cover the IAC port inside the intake area of the throttle body and the car idle will drop down to 800 and sometimes it will die, sometimes not.
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Covering the IAC port takes the IAC valve out of the equation... but to rule out if too much air might be getting past the TB butterfly valve (due to a messed-with idle stop screw), simply cover the entire TB opening while the engine is idling. If the engine still runs with all air being blocked from entering the TB, then there's definitely a vacuum leak somewhere. In this situation, there's no real point messing about with the IAC valve until you find where the air's getting in.[This message has been edited by Patrick (edited 07-07-2023).]
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buddycraigg
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JUL 07, 11:51 PM
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If you remove the IAC and cover the hole, it should stall.
If you remove and cover the IAC hole, and the top of the TB it should definitely stall.
I bet Patrick is on the right path, and you have a vacuum leak.
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Spoon
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JUL 13, 08:13 PM
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The most often placed missed for solving high idle on 2.8 is the cold air tube hidden behind and below the throttle body. It's a hard plastic elbow with o-ring seal that connects TB to the intake via a short section of rubber hose. My hose was mushy almost to a goooo feeling and the O-ring on the TB end was not a tight fit. At this stage it will always suck air and keep the idle high.
Another cause would be poor grounds between engine to body, engine to chassis, a weak or corroded negative battery cable, IAC connector dirty, etc.
see pic below,, Borrowed pic, Disregard the arrow. See item 5.
Spoon
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"Kilgore Trout once wrote a short story which was a dialogue between two pieces of yeast. They were discussing the possible purposes of life as they ate sugar and suffocated in their own excrement. Because of their limited intelligence, they never came close to guessing that they were making champagne." - Kurt Vonnegut [This message has been edited by Spoon (edited 07-13-2023).]
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Jeffdylanproctor
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JUL 13, 10:19 PM
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My car was having a very similar issue and it turned out to be the Coolant Temperature Sensor that was causing the high idle, as evidently the ECM wants the idle high till it reads a certain temp. These cars have two temp sensors, one that goes to the gauge, and one that goes to the ECM.
The one that goes to the ECM and causes the Idle issue is up right under the Thermostat housing. it is a little tricky to find and see, but it is very easy to remove. The factory plugs tend to have issues as well, and you can easily buy a plug with the sensor.
The high idle was driving me up a wall and this fixed it. Sounds crazy, but this sensor can cause a high idle.[This message has been edited by Jeffdylanproctor (edited 07-13-2023).]
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Patrick
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JUL 13, 10:31 PM
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| quote | Originally posted by Spoon:
The most often placed missed for solving high idle on 2.8 is the cold air tube hidden behind and below the throttle body. It's a hard plastic elbow with o-ring seal that connects TB to the intake via a short section of rubber hose.
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I'd say it's number two after a cracked EGR tube, but yeah, it's hidden away and easy to miss.
| quote | Originally posted by Jeffdylanproctor:
My car was having a very similar issue and it turned out to be the Coolant Temperature Sensor that was causing the high idle...
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You bring up a very good point, although a scanner or WinALDL would point out that issue pretty quick.
However, also keep in mind that a bad CTS would not enable an engine to idle at a high RPM with all air blocked from entering the TB (unless there was also a vacuum leak).[This message has been edited by Patrick (edited 07-14-2023).]
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ketstang
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JUL 26, 12:31 PM
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| quote | Originally posted by A_Lonely_Potato:
you can check that the IAC is functioning by setting key to ON with diagnostic mode pins jumpered. the IAC will audibly be etiher extending or retracting(i cant remember which.) shut off, pull out the IAC after ~30 seconds of this. then if the IAC pintle is extended, push it back in. repeat, and if it is extended the second time, you'll know its moving. |
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I followed your instructions and the pintle did move. So my IAC is good and working then?
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