Bad idle and fault codes BA

[El Andrew]

Hey guys

Anyone got a guess on this one? This morning I started up, idling for a minute or so while I did a couple of things, then as I put the car into drive, it started idling really badly (stumbling and shuddering).

Turned it off and on again and it went beautifully. Drove to work with no hassles at all - revved cleanly, made usual boost.

Grabbed the fault codes and got the following. All seem to suggest something was causing wacko sensor readings.

Codes relate to rpm/speed limiter reached and invalid speed and rpm readings. The u1900 code is usually there and I think relates to the obd device itself.

New cat, turbo, plugs and coils done in last six months, but nothing else significant. Stock tune, nothing else done. I reckon I might have pulled similar codes with coil related misfire under load last year, before I replaced them.

Scanned again after driving to work and no codes at all. Any ideas much appreciated!

[barnz]

u1900 is a comms code any is a bit general, can be a incorrect module, unplugged module, or just generated by flashing the pcm or an obd device like you say.

dodgy tps sensors are common on BA's resulting in crappy idle.

if its fine under wot I doubt its plugs or coils, was the replacement cat a stock item?

[Ralph Wiggum]

P2110 is telling you the PCM felt the need to limit rpm. This can be due to a range faults from (as mentioned above) dodgy TPS/dodgy PPS or even an Air Leak between the upper and lower manifolds. Anything that could cause the rpm to rise above the level the commanded by the pcm or lead the pcm to believe the TPS isn't in sync with the PPS.

 

[El Andrew]

Thanks guys! Cat is 100 cell.

I meant to mention that there is usually a SLIGHT roughness to the idle all the time,so thanks - checking for a manifold leak, tps or pps issue sounds like a good idea.

Actually my EL XR6 has had a rough idle since I bought it in 2004! Otherwise drives fine, but plugs, leads, fuel filter, thermostat, coolant temp sensor, o2 sensor and tps haven't fixed it. I've gotten past caring with that. Maybe I need to go somewhere and ask "can you vacuum leak test all of my falcons".

[El Andrew]

Would unplugging tps and pps make the pcm issue a default value, or just shut off the car? If I unplugged either of these and the idle stayed the same or improved, this would either eliminate or identify each of those as a possible cause

[camo86T]

Flame me if I'm wrong but I'm thinking 100 cell cat and stock tune won't like each other much

[barnz]

no tps data is probably going to put it into limp mode. 100 cell cat and stock isnt a great idea no....probably not the cause of a rough idle though

[El Andrew]

Haha we won't open that can of worms! I agree though, if the cat was going to cause issues it would be at WOT/sudden lift off rather than idling.

[barnz]

a tps sensor is like 90 bucks so not a huge gamble. your not going to be able to diagnose it by unplugging like an injector or coil, its going to upset sh*t. You could try logging tps and pedal position in an ignition on engine off state. They should be pretty much in sync. wouldnt trust logging during a drive as its normal for actual throttle position and desired to be different coz of all sorts of sh*te like torque managment ect

[jas98]

Mine did the same a while back. I changed tps and seemed good. Although it was perfect after I restarted. Also think it may have been cause I started it and waked it in drive pretty much as it started sooooo maybe that's why mine did it?