Rough Idle, Misfire 1mzfe
 

I have a 1996 Camry with a 1mzfe engine with 321K miles on it. To say it's been reliable would be an understatement. But all of a sudden it started idling very roughly and then generated a #6 cylinder misfire code. Then #6 and #4 and then the whole bank, and then #6 again. It changes almost every time I reset the codes but #6 always shows a misfire and the plug for that cylinder gets carboned up quickly. But no black or while smoke from the exhaust. Car passed CA emissions 2 weeks before problem arose. Again, this happened all of a sudden. Misfire happens with cold or hot engine. Past an idle performs ok (might be a very slight miss). I've thrown a lot of parts at it to no avail (thankfully nothing too expensive and again, I've spent virtually nothing (except normal stuff and CV joints) on the care in the 20 years I've owned it, so I don't mind so much. Yes, if I had more time, I would have tested more things before replacing, but in a car this old . . . The rough idle is a lot more apparent sitting in the car than looking at the engine directly. It idled high when the problem started but now is normal.

Here's what I've done:
1. Replaced both the fuel pump and fuel filter (never changed the filter before)
3. Replaced coils and spark plugs on bank 2
4. Replaced EGR valve and PCV valves. (EGR diaphragm was leaking and the PCV was very ugly)
5. Cleaned injectors (off the car) and swapped positions of them. Replaced o-rings and seals, no leaks.
6. Replaced coil connectors (all broke when disconnecting, the plastics on this car are very brittle).
7. Checked compression on that bank, results = #6-195, #4-200, #2-210 (way less than 20% diff)
8. Checked for vacuum leaks (propane check) - no leaks and replaced vacuum lines that seemed a bit loose.
9. Did a chemical block test (Results were negative but I'm not 100% the test was accurate as I think there was air in the system, plan to do this again)
10. Oil looks fine (not cloudy)
11. Vacuum gauge (other than slight twitch) was normal.
12. Cleaned throttle body and IAC valve (on my bench).
13. Checked and adjusted throttle position sensor
14. Replaced upstream O2 sensor
15. Short and long term fuel trim on bank 2 jumps around but is mostly negative. It's better than when I first started tinkering but still can run down to -18 or slightly more. Sometimes the short term trim looks fine. Some times the long term drops down to more normal (-3). But when it reads normal, its still shaking. Bank 1 is rock steady.

I have not tested or replaced the ECT, sensor but the engine doesn't overheat and the symptom are the same regardless if the engine is cold or warm. I haven't checked the fuel pressure on bank 2. Haven't had the injectors tested, but switching them around doesn't change the predominance of the #6 cylinder misfire code. Haven't checked the MAF (the OBDII data is in normal range)

Any Ideas? THANKS BEFOREHAND!!!

I can only share what happened on a different car. I was removing a clutch on 1999 Ford Contour SVT and thought it would be a good idea to power wash engine. Bad idea since car sat 6 months until finished and water did not dry out . Started it up, misfires and checked plugs. All rusty and plugs shot. It even misfired afterwards since some water was probably on top of the piston. Used a swab to get mine out with moving the position to TDC for ease of cleaning. Took a while still. Was there anything you did that contaminated the plugs. Were all plugs changed, Is Bank 2 front? The rears are hard but doable.

Hi, thank you for your response. The problem started all of a sudden and I hadn't done anything with the engine or car recently other than drive it. Yes, bank 1 is in the rear and I have changed the plugs on that bank (2 years ago), required a lot of flexible extensions, but as you say, it's doable. I replaced all the plugs in bank 2.

Any other codes besides those related to the cylinder number misfires?

No, after erasing the codes many times and driving around until new codes happen (probably 10 times so far), only #6 by itself or "random misfire" with misfire codes for #6,#4 and #2 show up. I haven't gotten any other codes. Thanks.

Ok, I just thought of a backfire with my daughters 2003 Avalon. High mileage used at graduate school.

I changed all the plugs and used old coils before she took it. A year or so later misfires and running terrible with engine light flashing. I sent her down my diagnostics module and narrowed it to one coil. Purchased a new coil and works fine ever since.

I think in the process of installing I may of put a hairline crack in it since this is the first time removing coils to get at plugs.

Hi WDC - Yeah makes sense it one of the coils was bad, but I replaced them all and swapped them more than once. I'm beginning to think that there might be a short somewhere in the wiring leading into the coil (or the wiring to the injectors), but haven't looked into that possibility yet. On my '85 Volvo there was a voltage drop of more than a volt from the alternator to the battery. The drop was caused by the battery cable to the starter motor. Cleaning the end connectors didn't help at all. It was internal corrosion (where the wire meets the connectors), replacing the cable fixed it. Just bought a temp sensor and a crank position sensor . . . Still searching for the fix!

I am sorry I missed that. You've done it all. I will be watching since I am very curious. I am praying for you since I know how "frustrating" this is.

If equipped, clean your maf sensor, check under the fuel intake manifold for signs of a rats. They get miffed with the fuel injector electrics and gnaw through them:D

Eureka! Fixed!
 

Haven't been able to work on it for a couple of weeks. Two weeks ago I installed a Schrader valve on the fuel filter banjo bolt and checked the fuel pressure (it was low (30lbs) but steady) with the engine on. Most everything I've read says the fuel pump operates when the key is in the on position, but on my car the engine has to be running (or turning over in the run position I suppose). When the engine was turned off the fuel pressure dropped rather quickly. I thought I might put a Mityvac on the fuel pressure vacuum line. When I did this the system was still pressurized (running). It spit gas out when I popped off the line. So I removed the FPR (car shut off and de-pressurized) and tested the diaphragm with the Mityvac. The pressure dropped quickly. I ordered a new FPR (Bosch) and installed it. It stumbled a bit at first but now it runs better than it has for years (not surprising considering the number of parts I threw at it!). Hooray! Theory: The FPR diaphragm was torn and gas was leaking into the manifold downstream from everything. It was liquid, not aerosol, so it flowed towards a particular cylinder, not all of them. It also explains why there was a PO306 code every time but PO304 sometimes and PO302 codes fewer times. PO306 alone or PO306 + PO304 or PO306 + PO304 + PO302 in descending frequency, but no other combinations of codes. BTW, the part I installed had a vacuum outlet tube that was substantially longer than the original. It was a bit of a bear to install to ensure there was no kink in the rubber line. Should I worry that the metal tube is longer than original? In any case, it's nice to have my Camry running well!