Hi, don't want to highjack the thread but I'm in the middle of something similar.

My local mechanic says it is trial and error and can be expensive if you buy new parts. My problem was with the cold start and intermittant engine symbol appearing. Car wouldn't tick over when cold. Once warmed up went perfectly other than random speedo readings.

Got a throttle body (£30) O2 sensor £30 and temp sensor £20 off local scrapper. Some error codes disappeared but the cold start persists. The mechanic didn't change the speedo sensor in the gearbox as he said it looked welded in.

Both scrap throttle bodies we tried caused crazy idling even when hot - so we've gone back to the original. Scrapper says they just bolt on but mech thinks they might need coding in (he hasn't got the codes)

New shape Fiesta Spring 2004 (dealer demonstrator) I'm back to square one. On warm mornings, no problem. Cold mornings, five minutes with foot on throttle until its warmed up. Mechanic says there is a hidden breather pipe behind the throttle body with a pinhole that causes it to collapse under acceleration. Possibly sucking in air, he's sealed it with silicone as it is a dealer part. No change.

Trial and error is OK but not at £35 per hour........

Hi, don't want to highjack the thread but I'm in the middle of something similar.

My local mechanic says it is trial and error and can be expensive if you buy new parts. My problem was with the cold start and intermittant engine symbol appearing. Car wouldn't tick over when cold. Once warmed up went perfectly other than random speedo readings.

Got a throttle body (£30) O2 sensor £30 and temp sensor £20 off local scrapper. Some error codes disappeared but the cold start persists. The mechanic didn't change the speedo sensor in the gearbox as he said it looked welded in.

Both scrap throttle bodies we tried caused crazy idling even when hot - so we've gone back to the original. Scrapper says they just bolt on but mech thinks they might need coding in (he hasn't got the codes)

New shape Fiesta Spring 2004 (dealer demonstrator) I'm back to square one. On warm mornings, no problem. Cold mornings, five minutes with foot on throttle until its warmed up. Mechanic says there is a hidden breather pipe behind the throttle body with a pinhole that causes it to collapse under acceleration. Possibly sucking in air, he's sealed it with silicone as it is a dealer part. No change.

Trial and error is OK but not at £35 per hour........

Is yours petrol or deisel?

petrol.

I had a similar problem to this and it turned out to be the coil pack that was at fault. Misfiring on cylinder no. 4

Was this an error code or was No4 plug sooted up?

not being funny mate, but why pay 20 notes for an unknown 2nd hand temp sensor when a brand new one wouldnt cost much more than that...have either temp sensors been tested, easy enough with volt/resistence checks

what engine are we talking about?

what codes is it throwing up now, if any.

Surely the codes must be painting some sort of picture, what happens if you start it up and give it a rev and then let it idle does it go like it should or just keep idling naff.

1.4 ecotec engine. It goes perfectly once up to temp. On warm mornings it starts with no bother. Anything less than about 5 degrees and it won't idle. Basically, it hasn't got a choke (for older viewers used to cars before ECU's)

I'll check on what codes were showing the last time it was checked.

The missus is getting hacked off with the speedo showing her doing 90 in the drive and the radio doubling in volume. Seems to be a particular problem when in reverse.

the sensor that decides when 'choke' should be applied is that temp sensor

not saying its the problem, but

a simple resistence check of the sensor itself is simple, cold engine, pull the plug, looking for approx 40k ohms across sensor pins, hot engine approx 6k....with your symptom, cold test is the only one you need to check.

alternatively, test the voltage

ignition on, plug connected, should be approx 3.5v at sensor on cold engine, 0.5 hot engine...5v or lower than 3.5, you have a bad sensor, if volts ok, then you need to check if ecu is receiving 3.5v as it could be a wiring/connection problem.