ROUGH RUNNING

[Pat Cooke]

Hi
My 1990 ZR1 has a fault which I am trying to identify.
The symptoms are:- it starts from cold and runs perfect, good miles per gallon, etc., when engine has been stopped for 15 mins it starts up running rough and the miles per gallon go down significantly, at tick over the fly wheel starts rattling. When left alone for 45 mins it starts up perfect. I have tried shorting the socket for the diagnostic and no codes appeared, I am thinking it is something to do with the oxygen sensor or a temperature sensor. I would appreciate any help.

[Schrade]

Welcome onto the boards there...

Maybe not necessary to start 2 threads on the topic.

Cold start doesn't tell much, and highway running doesn't either. WARMED up [Closed Loop] idle quality means more than anything IMO.

Rattling is likely the dual mass flywheel.

What makes you think O2's? Or Coolant Temp Sensor?

Do you have FSM for the car? And a multimeter?

[Pat Cooke]

Thanks for coming back to me.
Two postings was a mistake, I'm new here.
Yes, I think it is the dual mass fly wheel rattling.
I am not technical but happy to learn, what is IMO ?
Is FSM service manual ? I don't have multimeter but thinking of buying one.

[Kevin]

it takes a lot for the dual mass to rattle and 02 sensors won't do it. you could have failing injectors

[Schrade]

IMO = in my opinion...

FSM = Factory Shop Manual.

And a fuel pressure test, with leakdown time, is in order. How many miles on the car?

[We Gone]

Just a guess, could be a bad coil when hot.

[gbrtng]

Find a TECH 1 scanner so you can look at all the ECM inputs - this does sound like a failing coolant sensor, but better to be sure rather than throwing parts at it.

[Pat Cooke]

it takes a lot for the dual mass to rattle and 02 sensors won't do it. you could have failing injectors

Thanks ! You could well be right.

[Pat Cooke]

Just a guess, could be a bad coil when hot.

Thanks! I thought it was a coil and renewed them.

[Kevin]

Thanks ! You could well be right.

i should mention, I had bad o2 sensors on my car...last year I think it was, all it did was set a code but it wasn't running poorly and certainly didn't make the dual mass rattle. the dual mass will eat up a lot of vibration so having something rattle it takes quite a bit of vibration

[Pat Cooke]

IMO = in my opinion...

FSM = Factory Shop Manual.

And a fuel pressure test, with leakdown time, is in order. How many miles on the car?

22k 22,000 miles