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Discussion Starter #1
Hi everyone,

First, the good stuff:

CAR
2002 Mitsubishi Eclipse GT 3.0L (Manual)
Almost 190k miles

Problem
(Note that I've consistently had a P0421 for a few months)

Recently (since late December) when I've been driving, I've noticed some very occasional jerks in the car. It wasn't anything very regular but I had started to feel them while moving at constant speed.

Then a few weeks ago, I was driving down the highway and went over some rumble strips (placed to warn drivers to slow down) the second I came off of them, my car suddenly got 2 check engine lights: P0340, P0335 and the revs started jumping around like crazy.

I pulled to the side of the road and the car was idling fine. When I put my foot on the gas, the rpms were jumping up and down but the car would go back to a perfectly normal idle after I took my foot off.

I waited for a minute or 2 and then drove the car to a nearby gas station. I popped the hood and was trying to listen for sounds. It sounded like there might have been some strange noise coming from near the timing belt cover.

I went back into my car and checked my code reader again and I had a P0300 pop up. I shut the car off to do some googling and then turned it back on after a few minutes to try to inspect the problem further. It sounded fine and when I read the codes again, the P0340 and P0335 were gone.

I cleared the codes (at this point only 0300 and 0421) on my car and was able to drive it for 30 minutes /15 miles back home without any issues whatsoever.

ACTIONS TAKEN
I started reading into this problem and it sounded like it could be a crankshaft or camshaft sensor. However, I recently replaced the Distributor back in July and a mechanic had replaced the crankshaft sensor in September.

Despite that, I decided to inspect the crankshaft sensor and its connections. I took off the timing belt cover to inspect the sensor and it looks good, there didn't appear to be any issues with the cable either. I probed the connection for voltage and was getting about 12V, I then backprobe the sensor and it appeared to fluctuate between 0.4V and 4.2V perfectly fine when I manually turned the crankshaft.

I even tried bending/shaking the connecting wires as I did this to see if I'd lose connection. Unfortunately, this all checked out.

So now I'm wondering what the cause could be. When I last replaced my timing belt/water pump assembly (about 7 years ago @ ~140k), I believe I had some random idle/revving issues that led me to replace it initially.

Is it possible that my timing belt could be failing again and causing these issues?
 

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Huh. I've never had idle or revving issues with a timing belt. Usually it either works or it doesn't, which is when it breaks. Even if the tensioner were going, that shouldn't matter much until you skipped a tooth. They usually place them so they don't affect timing.

Maybe some of the more knowledgeable people can speak to the crank sensor and distributor thing. I know if you replace the distributor, you need to get the correct reluctor wheel depending on when your car was built, but I don't remember the specifics. Mine never failed. Also yours was working so I think it might be something else. Maybe a bad quality aftermarket sensor?

Sounds like a loose connection to me because of the rumble strip trigger. Unfortunately those problems are the hardest to replicate and track down. I would either wait it out and see if it happens again and do further diagnostics, or trace the sensor connections all of the way back to the ECU and make sure they're tight. A loose connection could be anywhere, not just in the engine bay, but I'd start there. Not an ideal scenario, but it'd be great if you could replicate the rough running and wiggle connections until you find what smooths it out.
 

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Sounds to me like you have an intermittent power issue.
The P0421 could be indicator that the P0300 may not be a spark misfire, but a fuel misfire or both. The cat is too cool. If it were a spark misfire, raw fuel would be hitting the cat and over heating it, not cooling it down. Seeing that this code has been active for a while though, you may just have a bad downstream HO2S or cat.. Check live data. Bank 1 downstream should hang right around .45v. If you're seeing the upstream and downstream reading the same, you have a bad cat. Seeing as you don't have a code for an HO2S, I would say you have a bad cat. This has 0 effect on running, but since is has to do with emissions, that annoying light will be on all the time.
The other 2 codes would be a result of voltage or signal drop on both sensors for 2 seconds or more....
I would start at fuse 3, which feeds the MFI relay.That fuse is hot at all times. MAKE SURE TO CHECK THE FUSE!!!! Pull it out and make sure the terminals are clean and closed. Look for arcing on the fuse blades or melting of the plastic as well. This is the fuse box in the engine compartment.
If that looks good, move on to the MFI relay and do the same thing. MFI relay powers the INJECTORS (possible random misfire issue), pin 47 and 59 of the ecu, IAC motor( possible reving issue), MAF sensor (possible running / reving issue), all 4 HO2S heaters, evap purge and ventilation solenoids, immobilizer, EGR and wait for it..........TDC SENSOR FOR THE DISTRIBUTOR (cam sensor) and CRANK POSITION SENSOR!!! Ding, ding, ding! All of your issues tie to this circuit... I have seen relays do some funky stuff. Work fine when cool, but heat'em up and boom.... Hit a big bump and boom........ I'll almost bet a paycheck it's either the fuse or relay.... I'm leaning more toward the relay though..... If all of that looks good, tappy tap tap that relay with the car running. If it acts up, problem found.. Now realize too that enough of a jolt WILL make a relay open even if it is good. There's always the possibility that is exactly what you had going on, specially with rumble strips. Harmonics are a bitch.....
 

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Discussion Starter #4
I appreciate the feedback, I forgot to mention that I did check my MFI relay (by removing it and hooking it up to a 12V supply in my house). I initially assumed that this would be electrical since it came and went so quickly, but after checking that relay and the crankshaft sensor I wasn't sure where else to look.

I'll definitely try to hit the fuse box while it's running to see and will also see about testing the relay while it's warm.

Ultimately, I've found that I've had a ton of electrical issues to fix ever since my voltage regulator went out on my alternator a few years back.

I'm not too concerned about the P0421 since it has been coming on and off for years (and I think a random misfire issue I had to drive the car on a few years back just about killed the cat (this random misfire was due to the distributor/ECU and I ended up replacing both - I'm assuming also a consequence of my alternator applying too much voltage to the system).

But yea, thanks for the suggestions and I'll update everything once I try them!
 

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Discussion Starter #5
Huh. I've never had idle or revving issues with a timing belt. Usually it either works or it doesn't, which is when it breaks. Even if the tensioner were going, that shouldn't matter much until you skipped a tooth. They usually place them so they don't affect timing.

Maybe some of the more knowledgeable people can speak to the crank sensor and distributor thing. I know if you replace the distributor, you need to get the correct reluctor wheel depending on when your car was built, but I don't remember the specifics. Mine never failed. Also yours was working so I think it might be something else. Maybe a bad quality aftermarket sensor?

Sounds like a loose connection to me because of the rumble strip trigger. Unfortunately those problems are the hardest to replicate and track down. I would either wait it out and see if it happens again and do further diagnostics, or trace the sensor connections all of the way back to the ECU and make sure they're tight. A loose connection could be anywhere, not just in the engine bay, but I'd start there. Not an ideal scenario, but it'd be great if you could replicate the rough running and wiggle connections until you find what smooths it out.
Timing belt: Yea that's exactly what I thought a few years back when I went to replace it. It seemed like a timing belt issue should only either work or cause huge problems. However, fixing the timing belt somehow solved my issue. I'll see if I can find my post on here about it.
 
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