2002 C70 Rich Idle Issues when Cold

[ryanvolvo]

1. Cold start fuel computation is based on the long term fuel trim value (LTFT).
2. Important data for use of lookup table in ECM are MAF and engine coolant temp (ECT).
3. Lookup table has to be correct.

If the LTFT is high (more than 1.10) then that should be dealt with. MAF, oxygen sensor(s), fuel pressure, inlet tract air leaks are items to check.

MAF has been repalced but could still be an issue.
ECT value should be read before engine is started with a capable scan tool. Some better generic tools will display ECT, MAF, and LTFT.

Everything may be fine but the performance reprogramming may be affecting LTFT and that is what the ECT factor is multiplied by to get injector opening interval for fueling for cold running.

Thank you for the detailed reply jimmy57 - this makes perfect sense so I thought I would do a bit of digging into the ECU to see what variables I could pull.

See the attachments below.

I have taken readings of ECT before starting the engine - you can see the comparison between that reading and also the ambient and intake temp readings.

I have also taken readings of LTFT variables before I reset the memory (there are a few of them so I'm sure you can make more sense of them than me).

I have also included the same variables after a memory reset (disconnecting battery and depressing the brake a few times).

I noticed that Long-Term fuel trim idle, bank 1 shows -2.20% before I reset them. What does this mean? After the reset it levels out to 0% on both banks and also all of the trims have been reset to 1.00.

Hopefully you can make some sense of all of this data and it may shed some light.

Sorry, I'm quite new to all of this. Thanks for your help in advance.

[ryanvolvo]

Which ETM is fitted to your car, if it is an early 02 model it could have the same Italian crap fitted to it as the 99-01 models which do fail needing the potentiometers replacing - Mike

I think I have the newer trouble free ETM. The car has done over 180,000 miles with the original ETM and while I have had issues in the past with rough idle, they were cleared by cleaning out the throttle body - which fixed it perfectly. I think I'd know about it now if it was the problem type. Also, the problem type exhibit rough idle even when warm - my idle issues are only when cold.

[ryanvolvo]

So after doing 100 or so miles since I reset the fuel trims, the readings have changed once more. Please see attachment for details. Can anyone shed any light?

[perkunas]

LTFT's look ok to me. Does the ECU enter closed loop? Also, no of the photos show engine temperature of 90C. Try to get the engine up to temp.

[misha]

Which ETM is fitted to your car, if it is an early 02 model it could have the same Italian crap...

That Italian crap is called Magneti Marelli.

Strange thing...Magnetti Marelli ecu(s) are known and proven to be good.There are a lot of european cars which use Magneti Marelli for engine menagement and never had a problem with them.

[misha]

You are in the right place, the C70 is covered through 2004 in this Forum!...

Ooops! My mistake...sorry!

[misha]

Here is relearning procedure i talked about:

computer relearn procedures.pdf

(33.82 KiB) Downloaded 125 times

Might be helpfull.

[ryanvolvo]

LTFT's look ok to me. Does the ECU enter closed loop? Also, no of the photos show engine temperature of 90C. Try to get the engine up to temp.

The engine has been run up to full operating temperature; I took those readings a few hours after.

How do I know if it has entered closed loop? What should I be checking?

Also, after the ECU adjusted parameters, I noticed "Long-Term fuel trim idle, bank 1 shows -2.20%" - why has it adjusted this?

Thanks for your help.

[ryanvolvo]

Also, the unstable idle still exists after resetting the ECU when starting from cold.

Actually, more specifically; after starting the engine I notice that for a few seconds idle is steady and then it starts jumping up and down and then finally settles out after 30 seconds.

[ryanvolvo]

I'm noticing smoke (not steam) out of the exhaust too. It clears after engine is warm. Can anyone shed any light?