My wife''s 00 SL1 automatic is bogging at idle and jerking and hesitating at speed. It did the same thing over a year ago and I took it to my local mechanic. They smoked the intake to check for a leak (which was what I thought it was) and hooked it up to the diagnostic computer. They didn''t find a leak and there was only an intermittant error in the diagnostic log. They did find carbon built up on the oxygen sensor and cleaned that off. After that it ran fine until last week. Any ideas? Thanks for your help.

They found carbon deposits on the O2 sensor, but failed to figure out why?

You have the classic symptoms of a faulty coolant temperature sensor. Bogging, hesitation, fouled O2 sensor and possible fouled spark plugs and the catalytic converter starting to clog up. All because a $14 temperature sensor is telling the PCM that the engine is colder than it really is.

Do you have a part # for the temp sensor? Also how hard is it to get to and replace?

Saturn Part #21025106

Located on drivers side of the cylinder head. Just below and to the right of the EGR valve. All you need is a deep 13mm socket. Should take 60 to 90 seconds to replace.

Thanks for the help. I just looked at the engine trying to locate the sensor. Isit located in a recess with two small gauge wires running to it?Edited by: Cestusrex

Yep, thats the one.

Replaced it this morning. I won''t have a chance to road test it until this evening but I ran it for a minute to check for leaks and it seemed to run more smoothly. Thanks for your help.

Well it still has the herky-jerkies. The sensor does seem to be working because the temp gauge is registering higher then it used to. The last timethe car did thiscleaning carbon off the oxygen sensor cleared the problem up so I pulled thefront sensorfrom the exhaust manifold, cleaned off some light soot, and reinstalled it. If that doesn''t solve the problem I''ll have to take it somewhere I can get underneath it so I can get to the rear sensor at the catalytic converter. Any other suggestions?

The O2 sensors could be fouled out again due to the faulty temperature sensor. Since you replaced the temp sensor, it shouldnt be running rich anymore. Cleaning/replacing the O2 sensors could solve the problem and since the temp sensor has been replaced, it shouldnt come back.

The herky-jerkies are rare now and it doesn''t do it at idle at all. I think the forward O2 sensor still has some carbon on it (the perferated heat shield over the end of the sensor makes it hard to clean off with an old toothbrush) or the rear one has some build up on it. I''m going to try some fuel treatment to see if that will help clean it out. Thanks for your help.