[FoeCom]

Hello. My car has recently developed a kind of misfire/starting problem. When starting cold the rpm rises up to 1500 and then drops. It keeps on falling right past it's normal idle point and stumbles around at 250-500. From there it either cuts off or goes back to 1500 to try the whole thing again. This goes on for maybe 30 seconds, then idles around 800-900. Also sounds a lot rougher at idle and when driving at low rpm.

I talked to someone on the phone from a parts supplier (forgot the name). They said it sounded exactly like the coolant temperature sensor. The symptoms showed up right after I reset the ECU and cleaned the air temp sensor. The air temperature sensor appeared to have a scorch mark on one side, but he said it couldn't be causing my problem. As from my previous posts, I've been having some trouble with misfiring under load, and have concluded that it has to be the fuel pump. (only thing I havn't replaced!

)
Could this just be the fuel pump getting worse?

 

[FoeCom]

Update. Thought I'd add what the check engine light is doing. It comes on when the key is turned right before ignition, then shuts off after 2 seconds or so. No blinking
Tried starting the engine to see if it would create a error. Did it's usual rev and die. Nothing on the check engine light.

 

[djtaylor]

That sounds like normal operation of the check engine light to me. It's a bulb/system test, don't all the other dash bulbs light up too then go out once the engine starts?

 

[johncc]

You can fairly easily test the coolant temperature sensor. You will need a multimeter, capable of measuring resistance, and a thermometer.

The idea is to remove the sensor (fairly easy) and test the resistance of it at various temperatures.

See this thread here, towards the end, for resistances.

The sensor is under the inlet manifold, at the back of the head. Not so easy to reach, but not the worst!

 

[FoeCom]

Yes, all the lights come on to show that they work when the engine is started. My computer's display light is dead so it can only be read at night with a flashlight.

The air temp sensor checked out fine, I'm going to wait until I get the new water pump before checking the coolant temp sensor. Is it possible that the ecu would not blink the check engine light even if the coolant temperature sensor is bad??? It runs rough even at normal temperature also. I'd really think this was a vacuum leak if the boost guage wasn't going well into the white. I can't see/hear any either.

 

[johncc]

I think it would depend how the sensor failed. If you got a short circuit or open circuit, or if the sensor was massively out of range, it would show a failure. If it's reading incorrect but allowable temperatures, it wouldn't detect it.

 

[FoeCom]

Re-gapped plugs, cleaned DI, cleaned the air temp sensor(again), reset ECU. Problem gone. Still fumbles around but more to the tune of 100 rpm + or -. Hey, I'm not complaning!! Although thanks for the suggestions.