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Topic
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Hi everyone,
2000 Mitsubishi Galant GTZ v6 – 135k miles – No engine lights
Symptoms:
After extensive driving (15-20 min) when I stop on traffic light and idle, the RPM gauge starts to fluctuate between 500 and 1000 RPM. The fluctuation is more noticeable after driving the highway in compare to driving the neighborhood. The very first drop in RPM is the biggest one – i.e right after I get to the full stop. After idling for a minute or two, the fluctuation tends to decrease a little bit. Switching from Drive to Neutral while idle puts RPM back to steady position at ~900 RPM with no fluctuation at all.
The car operates totally fine for the first 15 minutes of driving. Right after the engine starts, the idle is usually at ~1400 RPM and it gets down to ~900 when the car warms up. During these first 15 minutes the idle is steady, no power loss, no jerking, nothing.
In extreme cases the car might stall when the RPM drops too low. This case can only be reproduced after driving on the highway at 50+ mph and making a relatively sharp full stop. After googling this symptom, the most possible issue was pointed to be the transmission clutch converter solenoid getting stuck after locking on high speeds. However, I got this tested with a transmission auto shop. The guy had his computer plugged in and he didn’t see any TCC sticking. He said that transmission shifting looked good to him and the issue should not be related to the transmission.
What was tried/repaired:
– timing belt, water pump, spark plugs, wires and valve cover gasket were replaced a couple of months ago
– fuel pump was replaced at around 110k miles which assumes that the fuel pump should not be an issue
– throttle body, IAC valve and MAF sensor were cleaned as per FAQ, but didn’t help
– BG 44k fuel system cleaner has been used for a bad fuel injector case, but didn’t help
– all liquids were replaced relatively recently and are at the sufficient levels. Air filter was replaced as well.
– BG ACT+ transmission additive has been used for a version with TCC getting stuck. It seemed to have some positive effect but it didn’t fix the issueI checked this issue with two mechanics. The first one pointed this to be transmission related issue, which was a big concern of mine. However as I mentioned earlier, I tested this with the transmission shop and they overruled it. After testing all mentioned above, I have no clues what to test. Please help.
P.S. I’ve been trying to search the forum with similar issues but all other issues had slightly different symptoms than my case. I would welcome any helpful links that could relate to my issue.
Thanks in advance
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Replies
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it sounds like your iac is not keeping the idle up. I know you cleaned it but that does not mean it works right.
I’m not sure the voltages would be the same.If you have a working ac turn it on and see if the car idles
up and stays there.College man,
Can you clarify on “If you have a working ac turn it on and see if the car idles up and stays there”?
I turned ac on right when the RPM started to fluctuate at idle, but it didn’t have any effect. Did you mean to turn ac on before or right when the fluctuation is happening? How long do I have to keep ac to see any effect?
[quote=”kurt_” post=171454]College man,
Can you clarify on “If you have a working ac turn it on and see if the car idles up and stays there”?
I turned ac on right when the RPM started to fluctuate at idle, but it didn’t have any effect. Did you mean to turn ac on before or right when the fluctuation is happening? How long do I have to keep ac to see any effect?[/quote]
You could do both. Turn the ac on and you should see an immediate rpm change. (up)
or you could try the ac when the idle is going low and the ac demand should bring that
idle right up.College man,
Sorry for late reply, I got busy with other stuff. I followed your advice, but it didn’t have any effect. I turned on ac right when the RPM start to fluctuate and it kept fluctuate as it usually does with no effect on idle.
Few questions:
– What is the connection between bad IAC and turning ac? How does these two relate?
– If the IAC is actually the problem in my case, are there any other ways that I could check it?
– If it is not the IAC, what would be your other guesses besides it?Coming out of left field, perhaps one of the coils is flakey. Coils, as simple as they are, can go bad in strange ways. It’s possible for a coil to function perfectly when cold, but begin to break down when the engine heats up.
You say you aren’t getting any codes, which, on the surface of it, kinda rules out a failing coil. But, stranger things have happened.
[quote=”kurt_” post=172243]College man,
Sorry for late reply, I got busy with other stuff. I followed your advice, but it didn’t have any effect. I turned on ac right when the RPM start to fluctuate and it kept fluctuate as it usually does with no effect on idle.
Few questions:
– What is the connection between bad IAC and turning ac? How does these two relate?
– If the IAC is actually the problem in my case, are there any other ways that I could check it?
– If it is not the IAC, what would be your other guesses besides it?[/quote]When the car is in park and you floor the pedal does the engine rev strong or sputter?
I believe whats happening with your idle not staying at 750 with ac off the engine is wanting
to die from to low of an idle. With ac on the idle should go 800-900 rpms. which would come
from the IAC. It seems to have failed the ac test.I would also check for vacuum leaks… hoses and plastic pipes act diffrently when the engine gets hot…. might not be the problem but you can check when the engine is cold and see if that might be it
[quote=”college man” post=172246]
When the car is in park and you floor the pedal does the engine rev strong or sputter?
I believe whats happening with your idle not staying at 750 with ac off the engine is wanting
to die from to low of an idle. With ac on the idle should go 800-900 rpms. which would come
from the IAC. It seems to have failed the ac test.[/quote]College man,
Sorry for late reply. When the car is in park and I floor the pedal, the engine revs strong. No sputter.
Any other things that I could check? I really want to get to the bottom of it.
Rob781,
Thanks for the link. I tried to unplug my IAC when the engine is hot but I couldn’t get to it. It’s too far under the air hose and I need to take that off first before I can get to IAC.
Following up on my previous post.
Also, could someone by any chance advise a mechanic in Denver that could help me to figure out my car problem?
Thanks
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