timing belt changed now will only run at high RPMs P0300 code

[Josh39]

I have a 2005 and a pulley to the timing belt broke in january. Im in process of fixing the car now. We changed the timing belt, pulleys, and water pump. after the change i now have P0300 (random misfire/multiple cylinders). Now the car will start but heres the catch. you have to give it some gas to get it to fire. if you let off the gas it will die instantly, but if you hold the gas and keep it above 3000 RPM she sounds like a champ. I the changed the plugs and wires and Valve cover gasket. Problem still remains. I notice the air hose going to the air filter box is dry rotted. Could that be the issue? Vacuum Leak? I cant really check for a vacuum leak since i cant get her to idle. I was told that since she does fire that it isnt a valve or head issue. what can i do now to try to get her back on the road? Thanks in advance.

[avguy]

... I was told that since she does fire that it isnt a valve or head issue. ....

Don't know why someone would say that, especially with a misfire going on. The number and extent of valves bending is probably different each time one of these things happens, and perhaps you were "lucky" to only bend one or two just a bit. So you should do a compression / leak down test to see where compression is at. Now it's true that low compression would not definitely mean bent valves, because it could also be caused by a timing problem. So if the compression test comes back bad, the next thing to check is the timing to see if one of the 3 pullys is off by a tooth. If the timing looks good, bent valves then becomes the prime suspect.

[Josh39]

How do you check the compression? through the spark plugs? What psi should each cylinder be at? Also what is a leak down test? Would the timing being off still allow it to start? I just find it funny and confusing that she starts with the gas being pressed and stays alive at above 3000 rpm but below that she cuts off.

[Andrewsafb71]

How do you check the compression? through the spark plugs? What psi should each cylinder be at? Also what is a leak down test? Would the timing being off still allow it to start? I just find it funny and confusing that she starts with the gas being pressed and stays alive at above 3000 rpm but below that she cuts off.

There's so many issues that can cause a multiple misfire. What I did to fix mine was change the spark plugs and that tripped a more specific code a few weeks later. The new code was related to the MAP sensor and, foolishly, after the part came I noticed that the hose that goes to it was completely cracked. That was the only issue. The car has run great since. Maybe a hose broke while you were handling everything.

Fixing one issue may certainly reveal another. The issue may be unrelated to the timing belt, I'm no expert though.

Good luck!

[Josh39]

There's so many issues that can cause a multiple misfire. What I did to fix mine was change the spark plugs and that tripped a more specific code a few weeks later. The new code was related to the MAP sensor and, foolishly, after the part came I noticed that the hose that goes to it was completely cracked. That was the only issue. The car has run great since. Maybe a hose broke while you were handling everything.

Fixing one issue may certainly reveal another. The issue may be unrelated to the timing belt, I'm no expert though.

Good luck!

The little elbow joints to the map sensor i have had issues with for a couple years now just changed the joints every 6 months. Those are fine for now. The one thing i just noticed was, the hose going to the cabin air filter in dry rotted. Is that connected to any vacuum line? Like I said itll start and run over 3000 rpm and die below it.

[Andrewsafb71]

The little elbow joints to the map sensor i have had issues with for a couple years now just changed the joints every 6 months. Those are fine for now. The one thing i just noticed was, the hose going to the cabin air filter in dry rotted. Is that connected to any vacuum line? Like I said itll start and run over 3000 rpm and die below it.

If there is any leak in that it would certainly cause an issue. I believe it would trip a more specific code then P0300 if that was the issue but I didn't realize my MAP sensor hose cracked until the spark plugs were changed and I got the new code. Having the air filter housing and that hose in good shape is important anyway. Unwanted particles from outside that are bypassing the air filter and going into the hose can get into the engine.

My car would flat out die during idle at times and would poorly pick up speed, until I reached a certain amount of RPMS, before I fixed my leak issue. I can only apply the symptoms I had to yours and offer advice. I'm below a novice mechanic at this point lol.

[Josh39]

Ok so I just duct tapped the hose and it took longer than normal for the misfire to kick in. I started to see smoke come from the throttle body. Could the throttle body cause the P0300?

[Daox]

Are you sure that when you put the timing belt back on, you didn't skip a tooth on the belt?

[Josh39]

How can I check that. I had a friend do the timing belt.

[BrassBallsInc]

I have the same problem and I am certain it's not the belt being a tooth off. Nor is it a spark issue as I have swapped and checked each wire, plug and the coil pack. The car ran fine until the scheduled timing belt change. I changed the cam and crank sensors since the car has 300,000 miles now. Evidently the OP here doesn't have the mileage I do and did not change his cam/crank sensors yet has the same issue. It would be nice if he posted the solution he eventually arrived at.