The Top DSM Community on the Web

For 1990-1999 Mitsubishi Eclipse, Eagle Talon, Plymouth Laser, and Galant VR-4 Owners. Log in to remove most ads.

  • Join the Community!

    DSMtuners is a massive archive of DSM information - but more importantly, it's a COMMUNITY! Join in and participate with other DSMers, and invite all of your DSM friends to make this place their home. Chat with others, create a build thread, post questions and answers. Get involved! Logging in will also remove many of the advertisements, along with this notice. ;) It will also allow you to view images in threads.

Please Support ExtremePSI
Please Support Morrison Fabrication

2G 95 Talon TSi awd - High idle when hot

Rebecca_Kostya

Probationary Member
2
0
May 23, 2022
North Pole, Alaska
I’m a new member, first time poster here at DSMTuners. I have a 95 Talon TSi awd 5-speed with just under 100,000 miles on the Mitsubishi motor. I’m only the second owner, and have owned the car for three years. The first owner kept everything original, and so this car has had no modifications done whatsoever. I haven’t had to do much to keep it on the road so far, and I really love the turbo, so trying to take care of it the best I can. Overall, the car runs great, and I only drive it during the short Alaska summers to keep the mileage down.

It has one issue that I’ve noticed that I’m looking for some help diagnosing. It starts easily, and the idle when the motor is cool stays low and steady at about 800-900 rpm. After I drive it 20 miles on the highway (usually at 75-85 mph) the motor heats up, and the temp gauge stays in the normal range. It continues to idle normally during stop and go driving through town until I get to work. I park, let it idle for 1-2 minutes (because I read you’re supposed to let the turbo cool down?? Not sure if that’s true), then I turn it off.

The issue only shows itself when I start the car again before the motor has completely cooled (like 3 hours, unless it’s a hot day). When I restart the car, it starts easily, but begins idling at 1500 rpm. If i rev the motor, the idle rpm creeps up to even 2500. To be clear though, it does not surge. It holds steady at whatever idle it rests on. Getting on the highway and driving home sometimes helps, and when I arrive at home the idle is closer to 1200, but I’m assuming that the highway speeds are helping it cool down, and being cool helps the problem?

I have no idea what’s going on, and after asking lots of mechanics, I’m beginning to think it’s a Mitsubishi motor dsm quirk, so I’m hoping one of the brains on this forum can help me figure out what the problem is. Thank you for reading! Love this forum!
 
Last edited by a moderator:

pauleyman

DSM Wiseman
7,973
2,595
Nov 19, 2011
oklahoma city, Oklahoma
It's not electrically possible for the car to idle above 1500rpm. I'm guessing a physical problem. Check the throttle cable. They are known to slip out of the ferrules and hold the throttle open. Next time it does this open the hood and physically push the throttle plate lever to make sure throttle is closed. If it isn't find out what's hanging up. That's my best guess. If that's not it fill us in.
 

waltah

Proven Member
305
128
Mar 2, 2011
fairfield, Virginia
It's not electrically possible for the car to idle above 1500rpm.
Not to disagree but why is this so? If the Basic Idle Speed Screw (BISS) is out a couple turns too much or there's a small air leak then the Idle Air Control Valve (IACV) might be able to control the idle RPM with the car not too warm but under fully warm and heat soak conditions not be able to get the air flow down enough because it is all the way closed.

The ECU would never ask for a speed over 1500 but what if the valve isn't able to do as commanded?

I had the exact same symptoms as Rebecca on my GS-T: Normal idle under ordinary conditions but after getting it really warm and restarting it would idle 1500-2000 or more. Fixed it by cranking in the BISS screw a half turn at a time, then a quarter turn at a time until all was well -- maybe a couple turns total, I don't remember.

I think the book gives a specific procedure but I haven't done that yet.

I think there just aren't a lot of mechanics now who know how to set up the air on these cars. Or maybe virtually all prior owners tinkered without doing the research.
 
Last edited:

pauleyman

DSM Wiseman
7,973
2,595
Nov 19, 2011
oklahoma city, Oklahoma
Not to disagree but why is this so? If the Basic Idle Speed Screw (BISS) is out a couple turns too much or there's a small air leak then the Idle Air Control Valve (IACV) might be able to control the idle RPM with the car not too warm but under fully warm and heat soak conditions not be able to get the air flow down enough because it is all the way closed.

The ECU would never ask for a speed over 1500 but what if the valve isn't able to do as commanded?
At 1500rpm if the idle switch (or tps value) reports to ecu that throttle is closed, no matter what air comes in the ecu shuts fuel. Rpms drop and ecu catches and it starts all over again. That is why some cars idle surge. Is a car has an idle above 1500rpm then there is something else wrong.
I had the exact same symptoms as Rebecca on my GS-T: Normal idle under ordinary conditions but after getting it really warm and restarting it would idle 1500-2000 or more. Fixed it by cranking in the BISS screw a half turn at a time, then a quarter turn at a time until all was well -- maybe a couple turns total, I don't remember.

I think the book gives a specific procedure but I haven't done that yet.

I think there just aren't a lot of mechanics now who know how to set up the air on these cars. Or maybe virtually all prior owners tinkered without doing the research.
 

waltah

Proven Member
305
128
Mar 2, 2011
fairfield, Virginia
At 1500rpm if the idle switch (or tps value) reports to ecu that throttle is closed, no matter what air comes in the ecu shuts fuel. Rpms drop and ecu catches and it starts all over again. That is why some cars idle surge. Is a car has an idle above 1500rpm then there is something else wrong.
Ah ... 'fuel cut.' I didn't know that applied to idle. I think I've seen that surging in one of the Expos but it was a while ago. But I've also seen idles well above 1500 on my GS-T, and under circumstances like R. describes, particularly the hot day, parking for a while, starting again. And blipping the throttle made it worse. As she says, driving off makes things better, though when I got home the idle was still excessive.

Could vapor from the fuel tank cause the problem? What if the canister (activated charcoal or something) that is supposed to be absorbing those vapors. can't because it is too old? Where does the vapor go then? The situation described would be a 'lots of vapor' one.

I think the theory is the canister absorbs vapors at idle or stopped but during open throttle running air is sucked through it to purge and burn the vapors. But surely there's a provision for the vapor to go somewhere if it's not absorbed -- otherwise the tank would fail.

One could test that by opening the fuel fill a bit for a moment while idling to allow vapor pressure to bleed. If that temporarily relieves the too-fast idle then this is the problem. Wouldn't want to do that with a full tank though -- it could blow gasoline out the fill I think. Or while smoking or any other 'could ignite vapor' situation.

If this is the issue it would be much worse in sudden warm weather while 'winter' fuel (higher vapor pressure at a certain temp for easy starting) is still in your tank. 'Summer' fuels wouldn't be near as likely to do it.

We've got some 90+ days coming soon. If the problem shows up I'll try the test.

I wonder if those canisters are still available? I know the Expo ones aren't.

Otherwise what you're saying is this has to be something causing the Idle Position Switch to not report 'closed throttle' to the ECU. Cable jam, switch failure or Throttle Position Sensor not adjusted right. But any of those conditions would have enough other symptoms -- idle speed would often be wrong for one -- that it would likely be noticed.
 

pauleyman

DSM Wiseman
7,973
2,595
Nov 19, 2011
oklahoma city, Oklahoma
Ah ... 'fuel cut.' I didn't know that applied to idle. I think I've seen that surging in one of the Expos but it was a while ago. But I've also seen idles well above 1500 on my GS-T, and under circumstances like R. describes, particularly the hot day, parking for a while, starting again. And blipping the throttle made it worse. As she says, driving off makes things better, though when I got home the idle was still excessive.

Could vapor from the fuel tank cause the problem? What if the canister (activated charcoal or something) that is supposed to be absorbing those vapors. can't because it is too old? Where does the vapor go then? The situation described would be a 'lots of vapor' one.

I think the theory is the canister absorbs vapors at idle or stopped but during open throttle running air is sucked through it to purge and burn the vapors. But surely there's a provision for the vapor to go somewhere if it's not absorbed -- otherwise the tank would fail.

One could test that by opening the fuel fill a bit for a moment while idling to allow vapor pressure to bleed. If that temporarily relieves the too-fast idle then this is the problem. Wouldn't want to do that with a full tank though -- it could blow gasoline out the fill I think. Or while smoking or any other 'could ignite vapor' situation.

If this is the issue it would be much worse in sudden warm weather while 'winter' fuel (higher vapor pressure at a certain temp for easy starting) is still in your tank. 'Summer' fuels wouldn't be near as likely to do it.

We've got some 90+ days coming soon. If the problem shows up I'll try the test.

I wonder if those canisters are still available? I know the Expo ones aren't.

Otherwise what you're saying is this has to be something causing the Idle Position Switch to not report 'closed throttle' to the ECU. Cable jam, switch failure or Throttle Position Sensor not adjusted right. But any of those conditions would have enough other symptoms -- idle speed would often be wrong for one -- that it would likely be noticed.
If you have a high idle above 1500 I would suspect a miaadjuated tps or a throttle cable malfunction. Both situation tells the ecu throttle is not closed.

On a 1g I've have seen so many cars that did not have a functioning idle position switch because the owners eliminated the throttle body ground because they didn't know it was important. It's a small flat strap under one of the throttle body bolts and appears to have no purpose.
 

dwb

Proven Member
162
63
Sep 9, 2021
Broomfield, Colorado
Something is allowing too much air past the throttle plate. As others have mentioned, check your throttle cable (and cruse cable if you have it). If it's not that, perform a boost leak check. You might have a bad vacuum line or gasket/seal/o-ring that doesn't show up until it gets hot. If you don't find anything with the BLT, pull your throttle body and clean and inspect it. Make sure your throttle plate is tight and the shaft moves freely. Lots of information about the FIAV (fast idle air valve) out there as this is also a common point of failure (although those typically cause idle surge when they fail).
 

waltah

Proven Member
305
128
Mar 2, 2011
fairfield, Virginia
I park, let it idle for 1-2 minutes (because I read you’re supposed to let the turbo cool down?? Not sure if that’s true), then I turn it off.
It's in your owner's manual in the 'Starting' section.

"If your car is equipped with a turbocharged engine be sure to follow these precautions:

"1. Do not race the engine immediately after starting it.

"2. Do not shut off the engine immediately after it has been run at high speeds or under heavy loads.

"Allow the engine to run at idle for approximately 60 seconds or more before stopping it. Failure to do this will cut off oil supply to the turbocharger causing overheating of the turbocharger bearings."

The 'do not race the engine immediately after starting' is because doing so will cause seriously uneven heating which is very likely to damage something -- crack the manifold or turbo housing, maybe damage turbo bearings if oil supply isn't well established yet. Best to try to stay out of boost for a couple of minutes after you drive off.
 
Support Vendors who Support the DSM Community
Boosted Fabrication ECM Tuning ExtremePSI Fuel Injector Clinic Jacks Transmissions JNZ Tuning Kiggly Racing Morrison Fabrications MyMitsubishiStore.com RixRacing RockAuto RTM Racing STM Tuned VR Speed Factory

Latest posts

Build Thread Updates

Vendor Updates

Latest Classifieds

Top