UCF11 Celsior wont idle, hesitation and missfire.

[Stain]

I bought a UCF11 Celsior not long ago. It was using abit of fuel so I descided to send it for a service.
Only had the plugs/leads/rotors & caps replaced. Along with complete fluid flush.
Once I got it back the fuel ecconomy was much better, but it was pinging quite badly...
Under ANY load it sounded like someone was shaking a bag of marbles under the bonnet.
So I bridged the two terminals under the dash to check for a error code and got 24 (Intake Air Temp Sensor)
I read that a bad AFM is one of the main causes of pinging, so unplugged it...

However this is when the troubles started... once unplugged the car didnt want to idle... would just stall.
I held the revs at about 1500rpm for a few seconds and it seemed to fix that so I took it for a test drive.
It would hesitate and seemed to missfire under load... the transmission even went mental trying to go up a hill.
Didn't know which gear to be in, kept swapping between them constantly until I let off accelerator to lower the load.

It wasnt drivable so I took the AFM unit out all together and gave it a clean with some electrical contact cleaner
(starting to think that was a bad idea) I put it back together and reset the ECU. Now the car wont idle at all.
Holding the revs steady is impossible, it keeps surging at idle and if you release the accelerator pedal it'll just stall.
When free revving it sounds like its missfiring. If I try to drive it'll missfire even worse. At low revs/load it'll
surge quite badly and if I let off the accelerator it'll just stall even if the car is moving.

Problem is now it doesnt throw any codes. If I unplug the AFM it'll give 24 and 31. But with it plugged in, nothing.
During my testing I also tried free revving with the AFM disconnected and it'd surge like TPS wasnt set right
(would get to about 3k then drop back to 2k and so on) more acceleration would get past that point but I could feel it didn't want to rev.

I removed the spark plug covers to make sure the new leads were in the correct order and making good contact and all seemed fine.
I'm going to check if the timing belt has jumped a tooth tomorrow and try and source another AFM to test that.
But does anyone have any other sugestions?

 

[Amskeptic]

had the plugs/leads/rotors & caps replaced.
ecconomy was much better, but it was pinging quite badly...

So I bridged the two terminals under the dash to check for a error code and got 24 (Intake Air Temp Sensor)
I read that a bad AFM is one of the main causes of pinging, so unplugged it...

However this is when the troubles started... once unplugged the car didnt want to idle... would just stall.

This is normal behavior with an unplugged AFM.

took the AFM unit out all together and gave it a clean with some electrical contact cleaner (starting to think that was a bad idea)
Now the car wont idle at all.

This is not surprising with Karmann vortex generator AFMs, they use delicate laser/mirror to read light deflections in air turbulence. Get thee a Known Good Unit to test further.

Problem is now it doesnt throw any codes. If I unplug the AFM it'll give 24 and 31. But with it plugged in, nothing.
During my testing I also tried free revving with the AFM disconnected and it'd surge like TPS wasnt set right

I removed the spark plug covers to make sure the new leads were in the correct order and making good contact and all seemed fine.
I'm going to check if the timing belt has jumped a tooth tomorrow and try and source another AFM to test that.
But does anyone have any other sugestions?

I would suggest that you ratchet up your inquiry from simple to complex, but do not get ahead of yourself. Start with code search, yes, then check the dumb things that the workshop manual stresses, like looking at each terminal connector for proper placement within the connector, check for abrasions that finally broke through (particularly if you sublet the work to a shop: I do not know of a shop that willingly takes its time to do these complex cars correctly), and before you get too involved with timing belt synchronization, you will be right at the distributor rotors/caps/wires, double check them yet again. People put these rotors on bass-ackwards and they get their wiring confused frequently
bank < 2468 vehicle's right side
bank < 1357 vehicle's left side
right cap from center to outside 53C82
..left cap from center to outside 46C71

Good Luck!
Colin

 

[Peewee]

Actually if you unplug the AFM the car should still drive almost normally (assuming all sensors are working).

Perhaps your o2 sensors need changing?

I recently spent about $1000 trying to chase a rough idle. Ended up being a $60 o2 sensor.

 

[Stain]

Got the car sorted!

The timing belt hadnt jumped one tooth. It had jumped THREE!

So I purchased a timing belt kit with new pulleys, tensioner, etc and got about doing that horrid job. (WHY MUST THERE BE A HYDROLIC RADIATOR FAN! WHY!) 10 hours later it was back together.
Turned the key... acted exactly the same as before. Stalled over and over again.
Plugged the AFM back in, got AFM error straight away but now it would idle and rev without missfiring but still very hesistant at 2-3k rpm.
Since I was getting AFM errors but not IATS anymore I got a 2nd hand AFM, swapped that over and now its perfect!

The timing belt was pretty bad, no missing teeth but it was rather brittle and cracked.
So it must have slipped a tooth and started pinging, then I missed around with AFM and killed that by cleaning it at the same time the belt unfortantly slipped another two teeth.

Talk about a goose chase!

 

[gutbruito]

UCF11 Celsior wont idle hesitation and missfire

Check the TPS sensor, sometimes it will cause Hi Idle because ECM thinks throttle is being held open. use your scanners data to view TPS, PS switch and even AC operation.