[djsamuel]

I have a 2004 PT Cruiser with 261,500 miles. The engine and transmission are essentially original, with the exception of normal maintenance and an oil pressure switch and a belt tensioner.

I occasionally experience a misfire at idle, almost always when I come to a stop after running the engine at high RPM, such as having the car downshift while passing). The engine will misfire when stopped at a light, smooth out and run fine while driving, and then misfire again when I stop. Usually after shutting off the car and having it sit for a bit, everything runs fine when I start it up, and it idles smoothly. I normally get a P0302, P0303, or P0304 code if the CEL lights. If the CEL starts to flash, it goes out when I start moving again.

Last night, if was misfiring badly (after some higher speed driving). I checked the codes, and I had a P0300, with two codes pending (P0300 and P0304). The freeze frame data is:

Throttle Position: 14.5%, Engine RPM: 325, Load Value: 60.3%, MAP Sensor: 68 KPA, Coolant Temp: 176 degrees F, Intake Air Temp: 134 degrees F, Ignition Timing Advance: 10.0 degrees, Short Term Fuel Trim1: 0.0%, Long Term Fuel Trim1: -2.2%, Short Term Fuel Trim3: 50.0%, Long Term Fuel Trim3: 38.2%, Vehicle Speed: 0 MPH, Fuel System1: OPEN

I have changed the plugs and wires a couple of thousand miles ago. The car runs fine and accelerates fine. I'm leaning towards the fuel injectors since the are original, and I noticed that if I move them a bit, the problem seems to disappear for a while. In addition, the fact that the misfire location seems to occur in different cylinders at random times .makes me think that as well. I'm wondering if high speed operation causes the old injectors to have issues during normal operation.

Any thoughts, ideas, or anything indicated by the freeze frame data would be greatly appreciated.

Thanks,

Doug

 

[Bob Lincoln]

Probably not the injectors themselves, but more likely their wiring, or a ground connection. Check all of them carefully.

176F coolant temperature is low. How cold a climate were these measurements taken in? I'd expect more like 190F to 230F after a highway drive.

 

[ImperialCrown]

325 rpm is too slow. Fuel trims more than + or - 10% usually indicate a problem, likely related to the misfire.
Diagnose for high-speed misfire. As much as I hate to think it, I'm leaning toward valves not seating hot.

 

[djsamuel]

Probably not the injectors themselves, but more likely their wiring, or a ground connection. Check all of them carefully.

176F coolant temperature is low. How cold a climate were these measurements taken in? I'd expect more like 190F to 230F after a highway drive.

Bob, This was in the evening in Florida, about 60 degrees. I'd driven about 10 miles when the CEL was on. I do need to check the wiring more carefully. When I stopped it for a while, I pushed on the connectors at the injector. I was planning on replacing them, but when I realized it would take longer than I anticipated (since I saw I should remove the upper radiator hose for better access), I just pushed on the connectors for cylinders 2 and 3. Haven't had many error codes for them since. Need to try the same for cylinder 4, and at least I don't need to remove the upper intake manifold.

325 rpm is too slow. Fuel trims more than + or - 10% usually indicate a problem, likely related to the misfire.
Diagnose for high-speed misfire. As much as I hate to think it, I'm leaning toward valves not seating hot.

IC, I was worried about the valves as well. However, if the engine RPMs pick up, the misfire goes away. In fact, if I get the flashing CEL, it will stop flashing within seconds of pulling away from the traffic light, and often won't come back on when I stop at the next light. In addition, when I get an error code, it can be for various cylinders. If the valves are the problem, how can I go for days without this issue? I'm wondering if the valves rotate and can get into a position where they don't seat right. It is so intermittent; rare enough to be difficult to diagnose, often enough to be annoying and a concern. It may happen 1 to 2 times a week. I drive about 400 - 500 miles in a week.

Thanks for the help, I appreciate it.

 

[CudaPete]

Perhaps the timing belt has skipped a tooth? I think that someone on the PT board had a burned valve with similar symptons????

 

[djsamuel]

Perhaps the timing belt has skipped a tooth? I think that someone on the PT board had a burned valve with similar symptons????

The misfire is very intermittent. Most of the time, it idles very smooth. If however, I am driving fast (75 - 80 MPH), or have the transmission downshift while passing someone (high engine RPM), the car will occasionally be misfiring when I next stop at a light. If I shut off the car and let it sit a few minutes (around 5 minutes) the idle is usually smooth again the next time I start it up. Like I said above, I drive 400 - 500 miles a week, and the misfire may occur once or twice during the week (highway driving every work day - 70 MPH +). I may occasionally go a week or two with it never happening.

I should add, dumping a bottle of Techron in the tank will really help for a couple of tanks; extremely smooth idling regardless of how I drive. And, in all cases, the car has plenty of power all of the time, even when it is misfiring when stopped at a light.

Thanks for all the help. This is a frustrating one.

 

[AC TC]

Check pcv so it doesent suck oil when coasting.

 

[John Wood]

Is there an EGR valve on this engine? Perhaps there is just a piece of carbon on the valve seat or it is not seating properly. That could cause an intermittant condition at idle.

 

[djsamuel]

Just resurrecting this thread so I can provide an update and ask for more input.

After driving the car to NJ for my Dad's funeral, the misfire became a bit more consistent, although the car continues to run great at speeds other than idle. I am pretty much just getting P0300 codes now, no cylinder specific misfire codes. I finally got to do some work on it today. I changed the fuel injectors, as well as the spark plugs and wires, as well as the valve cover gaskets while I was at it (oil was leaking into the spark plug well). After finishing, the car starts right up and runs terrific, much better than before, but again not at idle. The car has a fairly distinct misfire when idling, although it is definitely not occurring each revolution of the engine. I may get several misfires in succession (once per rev), and then go 10 to 15 seconds without one. If I speed up the engine and return to idle, the engine will idle great for about 10 or 15 seconds, and then the misfiring returns. If I am driving and pull up to a red light, the car idles great, and if the light turns green fairly quickly, all is fine. If I'm stopped for a while, the misfiring returns and I get the flashing CEL.

Now here is something I found, and have no clue. When the engine misfires when I am at the engine, I can here a definite rush of air. I removed the air intake hose from the throttle body. If I put my hand over the throttle body opening so I can feel the vacuum; there is a definite and large increase in vacuum that coincides with every misfire. That increase is very short, and is just about exactly coincidental with the misfire. The vacuum returns to normal right away, until the next misfire, when the vacuum "surge" occurs again.

Just putting this out there in case anybody has any ideas. The engine has over 272,000 miles on it, so it could be any number of things. Like I said, the engine runs great, the car has plenty of power. It is just the idle that is screwed up.

Any thoughts on trying something like Seafoam? Don't know if carbon may be causing an issue with the valves. Have looked at rebuilt cylinder heads if necessary, and the cost isn't too bad, especially considering that for the amount of miles, my PT, both inside and outside, is in really great shape.

Thanks for any input.

Doug

 

[dana44]

This kind of sounds like it could be the AIC or IAC(can't remember the right acronymn, Idle Air controller), but it controls the idle air, and if it is sticking and goes low, it could miss. What with the number of miles, it would do as you indicate, run good off idle but could miss at low speeds.

 

[ImperialCrown]

This unfortunately has all the symptoms of a leaky valve(s). Compression sealing is less important the faster the engine moves, so poor valve sealing will show up more at idle/lower speeds. A compression test while cranking may also not show a huge difference between cylinders, but you may catch the low one.
A compression leak-down test with the engine stationary at TDC (valves closed) is the best indicator. With regulated air pressure applied to the cylinder through the spark plug hole, listen for hiss at the tailpipe (exhaust valves) or throttle body (intake valves) or oil filler cap hole (piston/rings).
Leaky valves can be intermittent and can show up more after a good, brisk highway run than around town as higher loads=higher temperatures and that can distort the valve head and/or valve seat and cause compression leakage. Leaky valves will burn and you might see the discolored metal spot at the valve margin/seat area where they are supposed to seal. They may be fine when cooled.
The exhaust valve runs much hotter than the intake valve which is constantly cooled by incoming fresh air/fuel.
At this high mileage and the possibility of valve seats also being burned, I would think that a reman head assembly is the easiest and best way out. You might want to have a live second opinion confirm our diagnostic findings so far.
The IAC may open more during misfire to compensate for the missing cylinder in an attempt to keep engine idle speed raised and stable. This would increase the hiss noise.
I'm very sorry to hear of your dad's passing. I'm watching my dad get more and more frail and shaky each day. Family is important, keep them close. It is one day at a time.

 

[djsamuel]

Just wanted to write a follow up to this. ImperialCrown hit the nail on the head with this one. I purchased a rebuilt cylinder head via the Internet from Cylinder heads International ( http://www.headsonly.com/ ) They did a really nice job, the new head looked great. I removed the old head to find burned exhaust valves on cylinders 3 and 4. Replaced the head and the PT runs like new. Below are pictures of the valves. Keep in mind, these are the original heads, and were never off of the PT in 281,000 miles. Very pleased with the service.

Cylinder #4:

Cylinder 3 - Note burned flat spot on exhaust valve (right valve on whole cylinder shown):

 

[chuzz]

Imperial Crown is definitely an asset to this forum. Nice call, man. I'm sorry to hear about both of your guys fathers. Mine passed on 24 years ago and I still miss him.

 

[dana44]

OK, burned valves are not a good thing. With this new found result, get your injectors cleaned or replaced. I say this because the only reason valves burn what with fuel/air ratios maintained through the computer, the only thing which burns valves is running lean. If you are running lean it means the injectors were the reason for it happening. Put the engine back together the way it is and the valves will burn again, something I have seen several other times if the injectors are not taken care of. Cleaning them (they sonic clean them) is cheaper than new ones, but I couldn't tell you how long injectors really last. I have one friend that has gone 350,000 miles with no problems yet, just a timing belt every 100K, so they do last a long time, so I am not against having them cleaned properly. Pouring injector cleaner is not proper cleaning by the way.

 

[djsamuel]

Thanks for the thought. I replaced all 4 of them with new ones.

 

[dana44]

Good. One less thing which could burn valves again. Repairs are expensive enough as it is, hate to see the same thing happen in another 10K miles.