Hi.

My 2001 LeSabre Custom 3.8 has cold start hesitation which goes away when the engine reaches operating temperature (10 min of driving 45 mph in Florida'* 90' ambient temps). I 'think' this may be due to a faulty ECT sensor located below the thermostat housing water outlet.

I don't have a meter so I haven't tested the sensor or the plug. Looks like the local parts store carries the sensor w/connector so I'm planning on getting that.

The sensor looks pretty accessible. Nothing in the way when looking straight in from the front - I can see the whole sensor and connector. Just not much room to swing a ratchet.

My main question is.. how much coolant (if any) will run out when the sensor is removed?

Not much should come out. Is the engine running rich or lean while warming up?

Thank you. I have no way to measure rich/lean. There is no fuel odor - the high warm-up idle and the operating idle are fine, there are no fluctuations.

You can measure the resistance of the sensor. What does 'has cold start hesitation' mean? Dead spot on acceleration or trying to start?

I don't have a meter to measure sensor resistance.

Starts fine. Engine temp at cold start-up is 78.

After shifting into Drive it still runs smooth - cold idle can pull car along at a creep and still be smooth.

The slightest touch on the accelerator brings on hesitation - a quick series of stumbles or what feels like misfires. Slightly more accelerator to get the car rolling up to speed begins with additional hesitation as before then quickly smooths out and continues to run smooth until taking off from the next stop, when it hesitates again as before.

All this goes away after 10 minutes of driving.

The car starts fine all the time and runs great after warmed up.

Two years ago, the car had a bad misfire and hard start. Replacing one coil corrected that. My 'cold start hesitation' feels nothing like that. It'* like a short series of quick pulsations - like a slight binding in a drive axle or u-joint. That'* how I imagine it, anyway, but it doesn't occur when car is rolling along at idle.

With warm engine while idling tap on the MAF and see if the engine stumbles or stalls. If so, it'* bad.

Will do. I'll get on it when I get back from my appointments tomorrow - around 3 PM. Thank you.

Wait . . . I haven't seen anything that condemns the ECT sensor.

Could be a lot of things with what we know about the car so far. First definitely the tap test on the MAF first because it is cheap and easy. Personally I'd go after fuel pressure next, then maybe TPS.

Regarding changing the ECT, you can keep a bunch of coolant in by plugging the hole with your thumb between sensors. Sounds funny but works well. You'll probably lose close to a gallon if you just let it run.

I finished up early today. After driving around town for an hour or so, I returned home and performed the tap test with the engine running at 191 F.

I used a medium screwdriver handle and tapped the MAF directly on top, all the edges, and various spots on the throttle body. This had no effect. Idle remained steady. I made another round, this time tapping a bit harder.. same results.

While I was in there, I tapped the air intake sensor and TPS. No change in idle speed.

I also tapped all the sensor connectors just for the hell of it - no change.

I tried something different this morning. The car started instantly, as usual. Instead of driving off right away while the engine was cold and the idle still high, I sat there idling for 5 minutes to bring the engine temp up. The idle dropped from 1000 to around 750-800 (dash tach reading). I then began to drive away.

The hesitation/misses were still there but not as pronounced. They were fewer and less intense - softer. They disappeared after 2 minutes of driving.

I also suspected the TPS a couple of weeks ago. I even bought a socket set for it. Then I read some info on the ECT sensor symptoms and those seemed to more closely resemble mine. So I pursued that angle and arrived here

I got my multimeter back and will try to get some readings on the ETC sensor when it'* cool in the morning.

I was looking around some more - the buickforums.com I think it was - and one person mentioned that a common problem with this vehicle was that over time
the TPS would develop a dead spot just off idle. That sounds like me, but who knows..

I want to test the TPS too but the procedures I've read call for two people - one under the hood.. one in the car. I may not be able to scrounge up a helper on this one. With 119K miles it probably wouldn't hurt to just replace the TPS altogether - forget the testing on that one