Xoferif

'91 3.1L mpfi

The problem -

Once the car hits 150-160*, it idles fine...but if you try giving it any gas, it'll want to stall. You can get it up in RPMs, but you need to fidget with it quite a bit.

When it's cold, it runs perfectly.

I've noticed that there's hardly any exhaust coming out when this happens. Which tells me that it's running too lean.

Also, it's not throwing any codes.

My first thought was that it was the coolant temp sensor (the one under the TB for the sake of clarity)...replaced it...didn't help any.

Also replaced the fuel filter...also didn't help any.

I'm 99% certain it's not the fuel pump.

Once it gets up to temperature, and you stall it...it starts right back up, and idles fine...but the moment you give it gas again, it's the same old thing (hmm...that gives me an idea...what if I give it gas as soon as it starts up and before it goes into closed loop...that'll tell me whether it's a sensor or the cat)...no huge black puff of exhaust coming out or anything. If you just let it cool down for 10 minutes or so, it'll cool down enough to run it fine until it hits 160* again.

So, I'm leaning between two possibilities....the o2 sensor or...possibly a clogged cat.

Would a shot o2 sensor cause it to be running lean? How would I test the o2 sensor to determine whether it's the problem or not?

I mostly just want to positively diagnose the problem before I start throwing parts at it.

Also, I've never driven the car on the road yet, but I've also never been able to get the gauge to read over 160*. I've replaced the thermostat already since the one that was in it was shot...that helped the temperature to reach 160* a lot quicker, of course, but that was all it helped...do you think that the gauge temp sender unit/fan switch/coolant temp sensor thingy in the driver-side head located behind the a/c compressor be the cause of all my problems, just this one, or isn't a problem at all? And I put in a 195* thermostat, incase you were wondering....Thanks...

2_point8_boy

First thing to do is to actually check your basics.

Do you have the proper fuel pressure?

Do you have a spark capable of jumping a 1" gap?

Is your ignition timing correct?

Until you answer these simple questions, it's pointless to go after things like a bad O2 sensor or clogged cat.