Rough starting

[russiankid]

For a while now I've been having rough starting after the car sat over night. It will start fine without any problems any other time but after it sits all night. It catches fine, but it will jump to 500rpm, run rough for a second or two, and then it will go to its normal cold idle. I have new fuel lines and fuel filter. There aren't any fuel leaks as far as I know. I am guessing it has something to do with the check valve in the fuel pump but I could be wrong. Any ideas?


P.S. Spark plugs have 9,500 miles on them and same goes for the valve cover gasket set.

[doglegleft]

bump... did you get your idle issue sorted out?

Here is my situation... very similar.

Recent work... cleaned the ICV and throttle body w/ all new gaskets, installed new plugs, new valve cover gaskets, new fuel filter, new air filter. Oil change.

First start after the tune up I expected the car to run horrible while the computer adjusted... it did so for a couple minutes and then the car ran great.

Next morning after sitting overnight / cold start, I had a rough idle (dropped below 500 rpm and stalled. Started again, rough idle for a minute and then the idle sorted out. I let the car idle in the drive for ten minutes and it ran well.

I thought the computer still needed to sort itself out to the tune up. Went for a half an hour drive to be sure all was well and then I loaded up the family and drove 900 miles from NC to MA yesterday to see the grandparents. We made 4 stops along the way without any issues. The car drove very well the entire trip

This morning started up the car and had the exact same idle issue.

BTW, No CEL.

I am going to go back to reading threads... could use any advice y’all got.

[LouieD]

I had a similar situation on my M20 car. Check the thermo sensor. Mine was way out of spec and gave me a world of trouble getting the car to run right in the morning, but once it got going it ran great.

[doglegleft]

I had a similar situation on my M20 car. Check the thermo sensor. Mine was way out of spec and gave me a world of trouble getting the car to run right in the morning, but once it got going it ran great.

I have the M50TU.

[katrina]

I am having the same problem. Sometimes it feels like I have a 454. The whole care shakes and it has really low rpm's and a really rough idle.

[XR000mb]

sounds like idle control valve or maybe clogged injectors?

[skylinergtr]

check the mass airflow sensor, run some injector cleaning, clean ICV, and clean Throttle body. Did any CEL come on? Another thing could be your coil packs are weak but i've never seen the issue when its cold. Usually when the car is fully warmed up.

[LouieD]

I have the M50TU.
Same sensor on both cars. It tells the computer the temp of the coolant and the engine management system reacts accordingly. If it's out of spec it will give the computer wrong info. Not saying that this exactly is your problem, but it's an easy item to rule out.

[doglegleft]

Same sensor on both cars. It tells the computer the temp of the coolant and the engine management system reacts accordingly. If it's out of spec it will give the computer wrong info. Not saying that this exactly is your problem, but it's an easy item to rule out.

Are you referring to the infamous coolant level sensor?

[russiankid]

Mine has been starting perfectly ever since I made this thread.

[LouieD]

Are you referring to the infamous coolant level sensor?
No. On your cylinder head there are two sensors side by side. They hide under the intake manifold right about #1 & #2 cylinder intake tracts. They look identical and perform similar tasks. One sends a signal to your temp gauge, the other tells the comp. the water temp.
IIRC the black one is the thermo temp sensor for the computer. That's the one that gave me trouble.

If you disconnect both, keep in mind that the connectors are interchange-able. So mark them before disconnecting. In theory the blue connector should go to the blue switch and the black to black, but sometimes they are covered in oil from a leaking VC gasket, so the colors are hard to see.