Issues with idle and misfire

C

cameronl

Member
Hey all,

Got an issue with my 2000 gli lancer coupe 1.5l manual. Stock engine with only a 2 inch tip.

It has an rough idle and small misfire.

What i have done so far to try fix the issue:

Replaced spark plugs (Tips where white and corroded
Replaced ignition leads
Replaced distributor cap and o-ring (contacts where corroded)
Replace fuel filter (leaking)
Replaced rocker cover gasket (leaking)
Removed ISC and cleaned that and TB/manifold with throttle body cleaner (used toothbrush to get right inside manifold)
Removed and cleaned TPS
Checked TPS voltages (.92v and 4.97v)
Checked throttle cable tightness
Completed oil flush and change
Bottle of injector cleaner
Bottle of valve cleaner.
Checked hoses and couldnt see any leaks but will look into getting a smoke test to confirm no vacuum leaks.

It will sit at 1200rpm when cold (as it should) and then slowly drop to 800 once warm (stock idle is 750 +/-100rpm). Once it goes below 1000rpm the revs started bouncing by about 150rpm when stopped at lights whether in gear or not. Every now and then it will drop to 500rpm or so then i have to press the pedal to bring it back up again. If i adjust the idle to 1000 it sits perfectly and doesnt jump or misfire anymore.

Could my ISC be on its way out?

I do need to get the timing checked properly due to removing the distributor to change the o-ring as well.

Any advise would be most appreciated.
 
Sounds like the IACV/ISC correct.
Have you changed fuels as well (possibly bad batch)?
Did you rub off the molyb grease on the rear side of the throttle body?
 
donki said:
Sounds like the IACV/ISC correct.
Have you changed fuels as well (possibly bad batch)?
Did you rub off the molyb grease on the rear side of the throttle body?
Click to expand...

Yes i have had 2 full tanks through it since starting the troubleshooting from 2 different servos. 1 tank 95 and the second 98.

Nah i just took the air intake of and sprayed the cleaner in then used the toothbrush and then a rag to clean it out. didnt actually take the throttle body or manifold off. You reckon its worth pulling apart fully and cleaning?
 
cameronl said:
Yes i have had 2 full tanks through it since starting the troubleshooting from 2 different servos. 1 tank 95 and the second 98.

Nah i just took the air intake of and sprayed the cleaner in then used the toothbrush and then a rag to clean it out. didnt actually take the throttle body or manifold off. You reckon its worth pulling apart fully and cleaning?
Click to expand...

I'd be leaning towards the ISC in this case. When its on its way out it makes idle especially cold idle, erratic. Any check engine lights?

Nah just a spray and run the engine is enough. The rear side of the throttlebody butterfly has a special grease on the rear of it that prevents vac leaks around it, it needs to keep this grease otherwise it has the same sort of symptoms. It will only come off with a solvent and some rubbing though.
 
Did the issue change or get worse after changing the distributor o-ring? Ideally you would have marked where the distributor sat before unbolting it, so it could be fitted back exactly the same.

If the problem didnt change since doing that, then stick with IAC as Donki has said.
 
Donki - No there is no check engine light coming on. Might give the intake another clean just to make sure.

SDate42 - RPM became slightly more stable after each item was replaced/cleaned (used to bounce around 300rpm before hand). Gonna see about borrowing a mates ISC and if that does fix it ill buy a new one.

Thanks for the help guys. ill let you know how it goes.
 
to check the ISC it is easy multimeter negative on middle pin (with 6 pin connectors) then test resistance (I think it was ~30 ohms) between pins 1/2, 3/2, 4/5 & 6/5 so +on 1 & 3 - on 2 then 2nd row + on 4 & 6 - on 5 if there is any (large) discrepancy between the 4 readings time for a new ISC
 
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