You may remember my problem...

car starts fine then about 1 min. after pulling out and driving ... hesitation, bog, backfire, stutter, etc. ...

then it runs fine until it cools down again and goes through the same process

so after doing all the usual stuff (flame trap, throttle body, cleaning clogged intake vacuum connections) it still does it.

long searching on the archives netted two theoretical causes for my problem:

1. Oxygen sensor - the post mentioned that when there is no signal from the oxygen sensor to the ECU that the ECU allows the time necessary for the sensor to warm up and then... when it still doesn't receive a signal from what it supposes to be a warm sensor it tries to use the bad signal until it becomes obvious to the ECU that the sensor is providing bad information then the ECU goes back to its default setting as in pre warmup. Causing the car to bog for the brief period that the ECU is trying to use the Oxygen sensor's bad signal.

I can't confirm that this is actually what the ECU is doing (nor do I know) but it caused me to check my Oxygen sensor with a meter and find out that it was not functioning properly - more following...

2. Intake manifold gasket leak - the post mentioned that a small leak somewhere along the intake manifold gasket occurs for a brief period of time until the gasket softens with temperature and then it seals the leak. This causes the poor performance during the short period that the leak is open.

Again I can't confirm that this type of thing does occur with an intake manifold gasket but I thought the idea had enough merit for me to consider testing it.

So after getting a bad signal from my Oxygen sensor I ordered a new one from FCP Groton and upon receipt pulled my old sensor off the car and found why it wasn't working... the "basket" of the sensor (with holes on it to allow gas in to the sensor's ceramic material) had broken off and fallen somewhere downstream in the exhaust. The ceramic material of the sensor was cracked and broken as well (God only knows what in the exhaust stream could cause enough impact to do this!).

with the new sensor in the car ran great, no bog during warmup since!

the gas mileage decreased a little bit at that point (2 mpg) so I thought I'd better check out my new sensor

I tested the new Oxygen sensor to make sure it was giving me the proper signal and it wasn't.... but that's another "FIXED" post that you may or may not be interested in!



Happy Jack

why happy? because I don't have to worry about my wife pulling out into traffic and the car not responding AND because I don't have to take my intake manifold gasket off for replacement! at least not yet....



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jack, Bad Blue, '86 245, 245,000 mi.