Bad Misfire Problem When Cold

The Problem: I drive a 2002 Toyota Camry 4-cylinder that I bought used in November. It now has 66,500 miles on it, and at the moment, the car misfires often and hard when it is absolutely cold then proceeds to get better (almost to the point of perfect) as the engine warms up. It can stall out when it is cold because it is misfiring so bad. I have been to two different dealerships at least six times for help with this, and no one can figure it out.

Technicians have diagnosed and/or fixed bad gas, a faulty coil pack, and a MAF sensor. They have thoroughly cleaned the fuel injectors, the throttle body and the top of the engine. All of the following tests have come back fine: differential pressure test, cooling system integrity, injector pattern, crank angle pattern, crankshaft timing, engine vacuum, vvt, coolant temp sensor. I have had the 60,000 mile service done, and the 65,000 mile service was just done during all of this. All of the fluids, filters and sparkplugs should be okay.

The next thing they want to do is start to tear the engine apart. Is that necessary at this point? They say they have tested everything that they can without tearing it down.

Any and all help would be greatly appreciated.


Daniel in Nashville

I didn’t see a mention of checking fuel pressure in there. Was it tested? Someone should find out whether or not all of the pressure bleeds off while the car is off and then observe how long it takes to get to proper pressure spec after it is started.

Was the engine vacuum also tested when cold? Was the idle air control valve cleaned/tested?

Is there a check engine light involved? If so, what are the error codes?

The check engine light us on and the codes are Cylinders 1-4 misfiring & random/multiple misfires. I don’t know the numeric codes off of the top of my head.

I don’t know if the vacuum was tested cold. The problem is that it warms up so quickly that they were having to let it sit for hours to duplicate the problem for testing.

I’m not sure about the fuel pressure. I want to say that it was but I would have to check. If it was leaking off how long would you expect it to take to build back up?

I’m not sure at all about the idle air control valve. How would this be cleaned?

Do you have the actual code? It will be in the format [P1234]

P300 - Random/Multiple Misfire
P302 - Cylinder 2 Misfire
P303 - Cylinder 3 Misfire
P304 - Cylinder 4 Misfire

Since the coolant temp sensor is within limits, I’d look at the spark plugs next. How do you know they are OK? Bad plugs can cause misfiring when cold, and be OK once warmed up.
I don’t think you are ready for a teardown, since it runs OK when warm.
Is it damp when the car is cold? That would indicate ignition wires.
Agree w/cigroller, test cold fuel pressure and cold vacuum.

Replacing the spark plugs was the first thing I did whenever the misfiring started which has been within the last 5-6000 miles or so. Could anything foul them so quickly?

If this shop is stating they have to tear the engine down to determine a problem without performing something like a compression test it would appear to me they’ve been doing a lot of guessing; and on your dime.

It’s absolute idiocy to even consider tearing into an engine without having a valid reason for doing so; as determined by a compression test. And if one assumes there is a compression problem (and on all cylinders to boot) then the point could be made that a compression test should have been performed as Step Number One. You ALWAYS weed out the possibility of a mechanical fault before replacing parts.
Odds are the engine does not have a mechanical fault. The purpose of the test is to simply make 100% sure that it doesn’t.

The fuel pressure is something I would definitely want to know here as the symptom could point to a lack of fuel or too much air. (as in a vacuum leak)

Did they check the compression?