2002 LS V8 Throttle Sticks and revs

[mvansant]

Over the last few months if I hit the gas pretty hard my throttle will stick. It revs to 3000 rpms and will not stop. I have to shut it off to fix it. Also it seems to be missing. When I get to around 40mph it either misses or hesitates. Any clue. I hope the hesitation is the not the transmission. It has 105k.

Mark

[shorod]

The sticking throttle could be build up on the throttle body or throttle plate. It could also be an issue with your throttle cable. You'll need to either inspect it or have it inspected.

The misfire could be a vacuum leak, need for a tune up, sensor issue, or leaking spark plug well seals. When is the last time a tune up was performed on the car? Have you pulled the plugs and inspected the coil boots for oil? Also, how old is the battery?

-Rod

[mvansant]

Originally Posted by shorod

The sticking throttle could be build up on the throttle body or throttle plate. It could also be an issue with your throttle cable. You'll need to either inspect it or have it inspected.

The misfire could be a vacuum leak, need for a tune up, sensor issue, or leaking spark plug well seals. When is the last time a tune up was performed on the car? Have you pulled the plugs and inspected the coil boots for oil? Also, how old is the battery?

-Rod

Rod,

Battery is a couple years old. It has never been tuned up so I thougth I would start at that point. I will let you know how it goes from there.

Mark

[mvansant]

Originally Posted by shorod

The sticking throttle could be build up on the throttle body or throttle plate. It could also be an issue with your throttle cable. You'll need to either inspect it or have it inspected.

The misfire could be a vacuum leak, need for a tune up, sensor issue, or leaking spark plug well seals. When is the last time a tune up was performed on the car? Have you pulled the plugs and inspected the coil boots for oil? Also, how old is the battery?

-Rod

Rod,

Finally my check engine light came on today. I went to autozone and it said cylinder 6 was missing. Do you recommend a tuneup or should they be looking for something else?

Mark

[shorod]

Perform a tune up and carefully inspect the coil on cylinder 6 for evidence of oil.

-Rod

[mvansant]

Culprit. Valve covers leaking oil into spark plugs. Ugh. Now I have a tuneup and covers.

[shorod]

Thanks for the follow-up. Also, be glad you have the V8, the tune up is quite a bit easier on the V8 than the V6.

-Rod

[mvansant]

Ok I am about ready to sell this thing. They did the tuneup and replaced the valve cover gasket. I drove it once and it drove great. I stopped for about an hour got back in it and it started missing again and when I tried to get on it it dogged it and then the reving started again. I called my mechanic back and said I think it is the coil. He said he moved them around but we will not know which cylinder is missing until the check engine light come on. Not real happy. This car has been alot to maintain over the last 6 years. I wonder if I should just sell it and cut my losses while it is worth something. What do you think is causing the throttle to stick? My mechanic said it would be very costly to replace the throttle.

[shorod]

On the 2003 and newer LS the throttle is electronic, and those are very expensive. On your 2002 it's mechanical and should be much easier to troubleshoot. Also, a professional scan tool should be able to monitor the misfire counts on individual cylinders even if the misfire counts are not high enough to trigger a diagnostic code. This access would be through the Component Parameters or PIDS.

You may want to have the shop check your fuel pressure under various conditions. If the fuel pressure sensor is working properly the professional scan tool should be able to monitor fuel pressure while driving. Maybe you have a weak jet pump which has been a topic of discussion on this forum recently as well. The PCM may be detecting a low idle speed due to low fuel pressure and speeding the engine up to compensate. One thing to try would be to unplug the Idle Air Control (IAC) when the engine is warm to see if the engine still idles at 3000 rpms or if it stalls. If the idle still is at 3000 rpms then you do have an issue with the throttle. If the idle speed is low or the engine stalls then you know your IAC is working and the mechanics of the throttle are not being held from closing fully.

-Rod

[mvansant]

ok, we replaced the tps and now the throttle is not sticking but now if you floor it lags and does pickup. We also tried the IAC but still missing. Any ideas?

[shorod]

If you can get access to a scan tool that can monitor individual cylinder misfire counts, that could tell you a lot about where to focus your investigation.

-Rod