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1G '93 Eclipse NA rough idle, high rpm and misfires - what could cause it?

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DjHOGAN

Probationary Member
4
0
Oct 17, 2020
Norderstedt, Europe
Hello everyone! I will skip the storys and get to the point (if you want 'em, let me know).
I posted this on DMStalk, now here to increase my feedback chance:

I got a 93' Eclipse 2.0L 4G63 DOHC N/A 152.000 KM and after sitting for about 3 years it has the following issues:
1. rough idle: RPM not constant, dipping around +/- 250 RPM
2. idle RPM too high at around 1200 when warm
3. inconsitant misfires, motor jerking every 2 or 3 seconds as if one cylinder fails to fire for one sequence / car jerking when rolling in gear after letting off the gas at 70km/h or slower

Other issues we found:
  • intake manifold black and smudgy on the inside
  • throttle body was dirty as hell (NOW CLEAN)
  • EGR valve was dirty as hell (NOW CLEAN and works)
  • engine is burning coolant in cylinder 3 (its damp, white smoke from exhaust)
Things we already did:
  • clean TB
  • clean EGR
  • replace sparkplugs & wires
  • replace oil and filter
  • replace fuel filter
  • replace all belts and water pump
  • replace valve cover gasket (was leaking)
My qestions:
- After cleaning the TB the car starts much better, but idle is too high, cant get the engine under 1000 with BISS anymore. There is a visible gap when looking though TB against the sky. Is there supposed to be a gap there or should it be closed completly? - If not, how big should the gap be?
-> I suspect the previous owner had the issue too, but instead of cleaning it, he adjusted the thottle position?

- Could the head gasket leak in cylinder 3 cause it to not fire sometimes? We looked through the spark plug hole, its not flooded but defently not dry. What else could cause the misfires and whats the best way to check for something like that?

- What is there to check for the rough idle? So far i know ISC, EGR, MAS and TB. Is there any particular oder in which to check these? And how? Because I do not own a analog voltmeter!

- We think that even before the car sat for 3 years, it was not serviced well. BUT i got some old paperwork from the previos owner:
EGR replaced 2013
ISC replaced 2013
Thats the only relevant parts to these problems that i found in there. There is not a lot we know about this cars history :/

Please let me know what you think. I will be happy to provide more information if needed.

!! - EDIT 18.10.2020:
  • ISC checked, resistance is correct between all pins and it vibritates when ignition is ON. Should it move a certain distance visibly? We took it out, applied 6V as stated in all the manuals, checked pins again. It twitched on every test, but very weak and hardly visible. Is it not supposed to move a lot more?
  • FIAV Wax Pellet element that expands when warm checked, closes correctly but airflow when cool is very very minimal (had it in the freezer for 10 min). Not sure, but it seems out of spec and feel like it should open more. Any ideas on that?

- Swapped vacuum lines to throttle body around, they seemed to be wrong.
Before:
A - Yellow
E - Green
P - Red
Now, according to diagram:
A - Green
E - Red
P - Yellow
Could that have been the cause for the super dirty EGR and intake manifold? Is that even the correct order now?

- Adjusted throttle position, TPS and BISS. Now the engine dies right after start but when i give it some gas and then let off, it stays on no problem, idling at around 900-700. Still rough but at least not too high. Note that the BISS is now almost all the way open.
 
I would check compression on #3. If you have coolant then I would say best case scenario you need a head gasket. I understand you may be trying to get it to run correctly before putting the effort of a headgasket in but if compression is low on #3 due to the headgasket then you may be chasing your own tail and the real issue is just that the car can't run when it's a cylinder down.

You may also want to drain the fuel tank. You may already have done this but I didn't see anything about doing that. 3 year old fuel is at the best starting to become stale and cars don't run well on old gas. There should be a screw on left side of the tank to drain the gas. DON"T pull the screw from the middle of the tank as this helps hold the fuel pump and you may not be able to get it back in without removing the pump to re-align the hole....ask me how I know
 
Thank you for your reply! We already got a new gasket and bolts here, hopefully we can get to it tuesday. I am sure thats gonna help, but not sure if it is the curpit for all the issues? I refilled the car full when i got it and we had it running for quite a bit now. Fuel gauge was at red before, so there should not be much old gas left. Good advice on that screw! Before i drove it home i took it to a shop, they changed the oil, filters and belts. Could the timing be off?
Now that its home, we can do a lot more ourselves.

I would love to get more detailed information on the ISC and FIAV. Because the are very hard to get in germany if at all, so i need to know if the work as intended.

Thank you for the input, but there is a lot left unanswered. We would love to know more!
 
It sounds like you have a vacuum leak causing your idle to raise. It's probably that space you referred to. You need to set the idle by grounding the timing connect on the firewall and adjusting the biss screw to the stock rpm (800?). You ground the timing because it can affect the idle and you don't want that to happen while you're setting the BISS.This is assuming everything is set and working correctly.
 
Okay i forogt to have the connector grounded. I will redo that, should help some more. But as i said in my edit, the TB valve is now completly closed and the idle seems correct. But the engine now dies right after start, it only stays on after giving it some gas.
 
Okay, thats what i needed, thanks. We will do correct adjustments tomorrow. I dowloaded every PDF here that i could find and my Haynes Manual arrived aswell. I could not find any very detailed info on the ISC / IACV? With the info i found i can only make it vibrate and click. How can i make it acutally retract and extend when outside the TB? I can not turn it by hand at all. I want to know if its stuck. Reistance on all the pins is fine, but i dont trust it.
We will install a new HG tomorrow, check for vacuum leaks and then work from there.
 
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