420A Misfire Issue

[onlytsuki]

Hello everyone,

I have a 1997 Mitsubishi Eclipse RS Auto with 97,000 miles and primarily all stock except the CAI and I've been struggling with a misfiring issue. On cold starts it would rev to 1000-1100 RPMS and fluctuate between 800-900. At times it would get as low as 700 RPMS when at a light.
Engine shakes violently, gas smells from exhaust, and engine surges and jerks when in drive after it is warmed up. I also feel considerable vibrations in my seat, pedal, and steering wheel.
I have replaced anything you can think off: Timing, mounts, plugs (gapped), wires, coil, IAC, MAP, TPS, Intake gaskets, fuel pump, verified all vacuum lines, injectors, fuel filter and regulator.
Additionally, I am noticing rattling noises from the exhaust likely due to a loose pipe coming into metal contact.
I wanted to ask if a possible leak from the exhaust could be the culprit of my issue or if it could be something else?

Thanks

 

[Turbski91]

have you done a compression test or a leak down test? Misfires are usually only caused by lack of air, fuel, spark, timing, and compression. I’m not a 2g guy, but if you replaced all of that, and the issue is still present i would start looking at compression values. Also is it throwing a check engine light?

 

[onlytsuki]

have you done a compression test or a leak down test? Misfires are usually only caused by lack of air, fuel, spark, timing, and compression. I’m not a 2g guy, but if you replaced all of that, and the issue is still present i would start looking at compression values. Also is it throwing a check engine light?

No check engine at the moment. I will try to check compression when I have the chance. Just trying to rule out what may be the issue. Thanks for your help!

 

[BLACK'98DSM]

Any idea where the exhaust leak is occurring? A leak before the primary O2 sensor would throw off the reading and cause it to run roughly.

 

[onlytsuki]

Any idea where the exhaust leak is occurring? A leak before the primary O2 sensor would throw off the reading and cause it to run roughly.

Not sure, I plan on either spraying some soapy water or running my smoke machine through the tailpipe and see if there is anything that may pop up. The exhaust does rattle when I slow down or when in gear and I remember the car beginning to have problems once that sound made itself known. Any insights?

 

[2gev]

fix that exhaust leak and verify your afr with a scan tool besides that, maybe crank sensor?

 

[onlytsuki]

fix that exhaust leak and verify your afr with a scan tool besides that, maybe crank sensor?

Will do once I get the chance, I will update if anything comes up.

 

[2gev]

Will do once I get the chance, I will update if anything comes up.

mine had a real rough idle and would lope real bad, turned out it was my o2 sensor bung was welded a bit to far out of the stream so i chopped it off and redid it and it runs perfect now, besides that what brand IAC did you go with?my car had a low idle or high idle issue and i tried prob 3 parts store ones and had 0 luck, found a throttle body in my parts bin with an oem IAC and threw it on and never had the same issue again, seems like oem for alot of the parts is the way to go for sure, plus you have no clue how long those parts have been sitting on those shelves

 

[onlytsuki]

mine had a real rough idle and would lope real bad, turned out it was my o2 sensor bung was welded a bit to far out of the stream so i chopped it off and redid it and it runs perfect now, besides that what brand IAC did you go with?my car had a low idle or high idle issue and i tried prob 3 parts store ones and had 0 luck, found a throttle body in my parts bin with an oem IAC and threw it on and never had the same issue again, seems like oem for alot of the parts is the way to go for sure, plus you have no clue how long those parts have been sitting on those shelves

I'm running the unreliable AutoZone IAC since my OEM IAC was not working as it should. Planning on switching to something else. Every sensor I have is from a reputable brand like NTK or OEM. Also I noticed some oil build up around my Camshaft sensor.

 

[BLACK'98DSM]

Also I noticed some oil build up around my Camshaft sensor.

The o-ring is probably leaking. Or the valve cover gasket above it. While that does need to be addressed, it would not cause the misfire.

 

[2gev]

I'm running the unreliable AutoZone IAC since my OEM IAC was not working as it should. Planning on switching to something else. Every sensor I have is from a reputable brand like NTK or OEM. Also I noticed some oil build up around my Camshaft sensor.

had the exact same issue with the duracrap iac , chased it for ever , if you can easily snag an oem used but working iac from ebay or a junk yard , you can test them with ohms with a multi meter