Hey guys, need some help diagnosing a problem. My truck, 98 Chevrolet P/U with the 4.3 and manual transmission, has an idle problem. When coming to a stop or shifting gears, it doesn't want to idle down. If I push in the clutch or put it in neutral, it will stay at around 2000 rpm's until I come to a complete stop. Also while in gear, you can feel it pulling you around like cruise control when in town. It doesn't do it all the time, but quite a bit. Seems like it does it more when running the a/c. Last year I replaced the IAC and cleaned the mass airflow sensor trying to cure it, but no luck. Anything else I should look for? Any advice is much appreciated, thanks.
Idle problem, 4.3 chevy p/u
- Thread starter womcat
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Inaccurate coolant temp sensor? Sometimes the coolant temp sensor will not let the computer know that the engine is warm enough to idle at 750 RPM.
A friend's S10 with the 4.3 had similar issues, and replacing the TPS cured all.
It hasn't thrown a code for this, and I'm pretty sure I've replaced the coolant temp sensor and the TPS a couple years ago. I might try another TPS, couldn't hurt. Thanks for the replies, would really like to get this annoying problem fixed.
Make sure your throttle body bore and plate and idle air motor are clean.
The TPS could cause this, if the problem still exists.
AC use DOES make the idle come down slower, but not to this extent.
And of course this also sounds like a vacuum leak. All sorts of lines , connections, and intake leaks to manually and tediously check.
The TPS could cause this, if the problem still exists.
AC use DOES make the idle come down slower, but not to this extent.
And of course this also sounds like a vacuum leak. All sorts of lines , connections, and intake leaks to manually and tediously check.
Originally Posted By: womcat
I don't have a scan tool, but might have access to one. Anything in particular I should be looking for?
Yes, look at the TPS voltage with the throttle closed. Most will read around .5 volts. If it's over 1 volt, it's toast. Also look to see if it moves evenly with throttle input.
You should look at the other sensor data and see if it jives with reality. Coolant temp with the engine cold should match ambient, barometric pressure should read high 28's to low 29's and so on...
I don't have a scan tool, but might have access to one. Anything in particular I should be looking for?
Yes, look at the TPS voltage with the throttle closed. Most will read around .5 volts. If it's over 1 volt, it's toast. Also look to see if it moves evenly with throttle input.
You should look at the other sensor data and see if it jives with reality. Coolant temp with the engine cold should match ambient, barometric pressure should read high 28's to low 29's and so on...
A problem that severe would have tripped a code.
Dirt and vacuum leaks are still #1 on my list.
Dirt and vacuum leaks are still #1 on my list.
Well I took the truck on a trip this past weekend, about 700 miles, and it did it worse than ever. I could push in the clutch while at highway speeds, and it wouldn't drop below 2300 rpms. The only time it would idle down is when i would come to a complete stop. You could actually feel the truck trying to accelerate without your foot on the gas. I did run the AC the whole trip, as it was hot.
Today I looked around the throttle body to see if there was anything obvious, nothing seemed to be wrong. Pulled out the IAC, it was clean and didn't seem gummed up. Throttle plate wasn't sticking.
I drove it some today, without the AC on, and it really didn't act up. I'm wandering if this isn't a computer problem. Maybe it's trying to idle up too much for the AC? I really don't want to start throwing parts at it, but I might.
Oh, and my source for a scan tool that reads live data is no longer available
Today I looked around the throttle body to see if there was anything obvious, nothing seemed to be wrong. Pulled out the IAC, it was clean and didn't seem gummed up. Throttle plate wasn't sticking.
I drove it some today, without the AC on, and it really didn't act up. I'm wandering if this isn't a computer problem. Maybe it's trying to idle up too much for the AC? I really don't want to start throwing parts at it, but I might.
Oh, and my source for a scan tool that reads live data is no longer available
Does it have an ambient air temp sensor? If the computer doesn't know how hot/cold it is outside, it may be running at 'high' idle(like when you start your vehicle for the first time of a cold morning for example).
EDIT: Appears to be perhaps behind the MAF along the intake?
Looks like one of these?
Just a thought...anyone else?
EDIT: Appears to be perhaps behind the MAF along the intake?
Looks like one of these?
Just a thought...anyone else?
Originally Posted By: The_Eric
Replace one at a time...
^I agree. Check the voltage at the TPS first, and if it's good then look at the other. Looking for a any sort of vacuum leak would be a worthy cause as well.
As a side note, on my dad's 4.3 in a 2001 Chevy S-10...just changed the oil and fuel filter(unknown mileage on filter) and the mid-upper power was noticeably better.
Replace one at a time...
^I agree. Check the voltage at the TPS first, and if it's good then look at the other. Looking for a any sort of vacuum leak would be a worthy cause as well.
As a side note, on my dad's 4.3 in a 2001 Chevy S-10...just changed the oil and fuel filter(unknown mileage on filter) and the mid-upper power was noticeably better.
Alright, finally got around to messing with it. I replaced the TPS, which was only a couple years old, and it has seemed to fix it. Drove it some today, and without the AC on, it idles down quickly like it should. With the AC, it takes a second longer to idle down, but no where near as bad. I can now push in the clutch at speed, and the idle will actually drop. While I was at it, I also replaced the air temp sensor because it was cheap.
So the truck is running great again, really appreciate all the replies. This site is great!
So the truck is running great again, really appreciate all the replies. This site is great!
^Awesome, thanks for sharing the update. As it goes with cars, there's a good chance you'll be back regarding this or another vehicle.
+1 for success!
+1 for success!
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