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

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.

Quote:

---

Originally Posted by Josh39

... 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.

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.

Quote:

---

Originally Posted by 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.

---

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!

Quote:

---

Originally Posted by Andrewsafb71

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.

Quote:

---

Originally Posted by Josh39

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.

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?

Quote:

---

Originally Posted by 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?

---

What do you mean exactly by "kick in?" Did the check engine light come on? If it's a misfire that makes the light stay on for a duration and then off sometimes it's a type 2 misfire which if I remember correctly does not involve the catalytic convertor. If it did it would be constantly flashing and that's a problem.

Did the engine light turn on and remain on when you say kick in?

How much smoke? What color smoke? Did you drive to the point where everything under the hood got hot? Details! Don't rely on that duct tape for the moment, replace that air duct if you have any doubt it's not as it should be. Even if it doesn't solve your misfire problem. You can get an OEM part off the internet for about $9. Garbage getting sucked in the engine bypassing the air filter is bad bad news.

Replace the hose and try cleaning the throttle body. It may not fix the misfire problem but it will be an improvement with how it's driving The throttle body does not need to be removed to clean it, just look up a tutorial video. If you have a friend handy or something you can put on the accelerator while you clean it to open the throttle it will make it easier then pulling on the end that opens it.

Without resetting the computer the car has to be driven a certain amount of miles for the computer to report that the misfire is gone. The computer can be reset by unhooking the battery terminals for about 10 minutes. The computer will reset to the default factory settings and will take time to calibrate to how your engine is performing, your car will most likely ride differently until it has adjusted from what it's supposed to be performing at versus how it's actually running.

Use caution resetting the computer, everything will be back to normal after driving for a while but you'll know for certain if the check engine light, again after driving it for a bit, comes back on because of a misfire.

Quote:

---

Originally Posted by Andrewsafb71

What do you mean exactly by "kick in?" Did the check engine light come on? If it's a misfire that makes the light stay on for a duration and then off sometimes it's a type 2 misfire which if I remember correctly does not involve the catalytic convertor. If it did it would be constantly flashing and that's a problem.

Did the engine light turn on and remain on when you say kick in?

How much smoke? What color smoke? Did you drive to the point where everything under the hood got hot? Details! Don't rely on that duct tape for the moment, replace that air duct if you have any doubt it's not as it should be. Even if it doesn't solve your misfire problem. You can get an OEM part off the internet for about $9. Garbage getting sucked in the engine bypassing the air filter is bad bad news.

Replace the hose and try cleaning the throttle body. It may not fix the misfire problem but it will be an improvement with how it's driving The throttle body does not need to be removed to clean it, just look up a tutorial video. If you have a friend handy or something you can put on the accelerator while you clean it to open the throttle it will make it easier then pulling on the end that opens it.

Without resetting the computer the car has to be driven a certain amount of miles for the computer to report that the misfire is gone. The computer can be reset by unhooking the battery terminals for about 10 minutes. The computer will reset to the default factory settings and will take time to calibrate to how your engine is performing, your car will most likely ride differently until it has adjusted from what it's supposed to be performing at versus how it's actually running.

Use caution resetting the computer, everything will be back to normal after driving for a while but you'll know for certain if the check engine light, again after driving it for a bit, comes back on because of a misfire.

---

That's just it I can't get it to stay on to drive. I let off the gas and she dies. The check engine light is flashing with the hold light while I have the gas down to 3000 rpm in park. It was a little white smoke. I removed the air hose thing and the smoke was coming from the throttle body with a strong gas smell. Could it be my intake manifold or should I say the hell with it and try the head replacement and just hope it was a valve issue?

Quote:

---

Originally Posted by Josh39

should I say the hell with it and try the head replacement and just hope it was a valve issue?

---

Before you get too radical, go back to basics - run a compression test and put a vacuum gauge on it. If the compression is low or the vacuum gauge fluctuates on crank, then I would look at valve sealing. If it is all good, the problem is likely external to the head. This is assuming the valve timing is correct.