Stock 1gt Idles rough, bucks, dies, and more

[RedFoo]

The car is a 92 Laser RS, bone stock. The car will usually idle, although it sometimes dies. Once driving the car will buck and has no power. The boost gauge almost always shows 7+ lbs of boost, even during known vacuum.

I turned up the idle using the set screw to around 2k and after the engine warmed up fully it drove very well under gentile driving conditions.

I already did a pretty thorough search for intake / vacuum leaks and patched whatever I did find. The check engine light is also on but I have not pulled the code yet. Tomorrow I will limp it onto my lift so I can dig into it with my real tools tomorrow and come back with some sensor readings and a code for you guys.

Where does the stock pile of a boost gauge get its signal from on the 2.0t

 

[Rsawd95dsm]

Its an electronic gestimate from the ECU. Its not even a real vacuum/boost gauge. Try giving it a BLT.

 

[RedFoo]

Okay I got the DRBIII hooked up and played with my toolbox quite a bit today.

The ignition timing is being retarded 12-16 degrees by the ECM and there is a knock sensor code. The knock sensor was (somehow) significantly damaged. I have another one coming. I also did some more testing and could not find any more intake / boost leaks. I did find a coolant leak. I also noticed that while the engine is cold it will (rarely) missfire. It never misses when the engine is at operating temp that I can tell.

All other sensor readings on the scan tool show totally normal.

Engine timing is on. Forgot to mention that.

 

[RedFoo]

Okay so I replaced the knock sensor since it was the only thing the scant tool showed as being off. I reset the ignition timing and idle as per the mitsubishi service manual. I checked it AGAIN for any leaks and found nothing. I drove it for several hours after all of this flawlessly. Parked it outside, started it in the morning... same problem. It bucks and misses under anything above a high idle. It idles (mostly) smooth now. If I park it in a heated garage, no problem.

ECT shows normal readings on the scan tool.... I'm really so confused.

 

[Xploitn]

Parked it outside, started it in the morning... same problem. It bucks and misses under anything above a high idle. It idles (mostly) smooth now. If I park it in a heated garage, no problem.

ECT shows normal readings on the scan tool.... I'm really so confused.

Is that behavior only occur before it gets to operating temperature? Once it's up to operating temp, does it run normally?

 

[RedFoo]

Yeah only when cold. Perfect at 192 degrees. ECT sensor gives normal, reasonable readings 24/7.

After I let it warm up I drove it for over an hour in town and highway. It drove like a perfectly normal car.

 

[Xploitn]

I know you said the car is (mostly) stock but are all of the vacuum components still installed? Specifically the fuel pressure solenoid. (normally it helps with warm starts so it might not be the issue)

From what I know it's fairly common, more so when you do the vacuum mod. When you delete the sensors on the drivers side of the engine bay it really does it.. All of my cars have done it. One of the sensors on the firewall on the drivers side is a cold start vacuum solenoid that actuates vacuum when the ECT is low so it won't run as rich and buck.

 

[RedFoo]

Interesting. To my knowledge the vacuum system is fully intact, but I will do a double check for that.

 

[Phantom DSM]

Interesting. To my knowledge the vacuum system is fully intact, but I will do a double check for that.

Check out this vacuum routing diagram if it helps. The 1g version is in middle 1g before http://www.dsmtuners.com/forums/art...-speed-shop-vacuum-diagram-removal-1g-2g.html Check the ECT on the thermostat housing sensor per service manual ohm readings with a voltmeter when cold, is it within spec? Also does it have new spark plugs..if you can pull one out and let us know what it is. Nice stealth by the way

 

[RedFoo]

Thanks! I love the Stealth. It was my dream car since I was 13. ECT sensor is good. Vacuum is intact. Plugs are brand new NGK Iridium. I have had a few people go NOOOO GET COPPER RIGHT MEOW. Are they right?

I'm really running out of ideas here. Does anyone else think its time to open up the ECU?

 

[Xploitn]

Unfortunately I have run out of ideas and all other info points to the ECT or possibly FP solenoid. Maybe try swapping a known good ECU if you have a buddy with one locally.

IIRC correctly, Iridium is good. I believe it's the platinum ones that we want to avoid like the plague.

I believe the discussion around the NGK Iridium plugs is that they don't make a big enough difference compared to the much higher costs compared to the copper NGKs.

 

[RedFoo]

Thanks for the help and I am sorry for the late reply. I dont have access to a known good ecu sadly. I am also totally out of ideas. I guess the fix is to let it warm up before driving. Ive even let a couple master techs play with it and they are equally baffled.

I really dont want to give up on it. The body is one off from perfect. It would make a great DD if the car wasn't being such a stubborn little bi***.

 

[jukebois]

check the air pipe between the mass air flow turbo for looseness or cracks.