Cold start idle too low, stalls 420s

[Ant2]

This weeks issue, subsequent to the TPS sensor and lambda being replaced due to being faulty (caused 2k idle, throttle hesistation, surging etc)

It now idles too low on cold starts.  I.e if temperature is under 50c and car has not been driven in past 2+ hours.

It idles  700-800 rpm and will stall unless I keep my foot on the gas to bring it around 1k and I have to keep itnl like that till the car reaches 50c. I.e 2-3minutes. Subsequent engine restarts still has the same issue.

 

This is odd as prior to the last tps and lamda issues my car idled around 700-1k and never stalled.

When I was searching the forums I read about trying an ecu reset.

I tried disconnecting the neutral for a few minutes as I read the tps can get set to incorrect position,  this didn't help.

It can't be the new lamda as this wont function till hot and shuts off after subsequent restart.

the only other thing I read involved buying the ecu lead and easimap to read the tps voltages to see if they are set correctly.

 Any other ideas that don't involve another day travelling to the garage?

Example: 

 

 

I get no issues if car has been previously warmed up i.e even after an hour it's fine as long as the engine is warmer than 50c.

[aerobod - near CYYC]

There is no ECU reset on the MBE 9A4 that will affect the idle at cold start or change the TPS calibration.

The TPS has a very small adjustment within the mounting holes that could affect it. Without Easimap to view the voltage and throttle site, you could slacken the screws just enough to move the TPS, start the engine, then rotate it within the holes to see if the idle improves in any position, then re tighten the screws in the best position.

[Ant2]

6 minutes ago, aerobod - near CYYC said:

There is no ECU reset on the MBE 9A4 that will affect the idle at cold start or change the TPS calibration.

The TPS has a very small adjustment within the mounting holes that could affect it. Without Easimap to view the voltage and throttle site, you could slacken the screws just enough to move the TPS, start the engine, then rotate it within the holes to see if the idle improves in any position, then re tighten the screws in the best position.

Thanks for the information.  The adjustment that is made from fitting does this only effect the cold idle or hot idle as well?

Reason I ask is that it's idling nicely when hot, if I adjust it without viewing the voltage I don't want to cause some other issue as I'm sure they checked the car on easimap after it was swapped over..

[aerobod - near CYYC]

1 minute ago, Ant2 said:

Thanks for the information.  The adjustment that is made from fitting does this only effect the cold idle or hot idle as well?

Reason I ask is that it's idling nicely when hot, if I adjust it without viewing the voltage I don't want to cause some other issue as I'm sure they checked the car on easimap after it was swapped over..

On hot idle it will be less sensitive and should be close-loop controlled to the target idle. The cold idle should be higher than the hot idle by a couple of hundred revs to avoid stalling.

If you have a pen that is visible on the black TPS body, you could put a reference mark on it to the throttle body to return to the original position before moving it.

[aerobod - near CYYC]

One other issue you may have with the new TPS is that it has a different calibration of voltage vs angle than the original likely Colvern CP17 one. Just swapping the TPS won’t work without a new TPS to voltage map. The idle adjustment is very sensitive to changes of only 0.02V or so. To make this change requires knowing the original TPS voltage at idle and full throttle and adjusting the map to ensure the new TPS gives the same voltage at those positions. It isn’t just a mechanical change unless the voltages match exactly and requires Easimap to change.

[Ant2]

20 minutes ago, aerobod - near CYYC said:

One other issue you may have with the new TPS is that it has a different calibration of voltage vs angle than the original likely Colvern CP17 one. Just swapping the TPS won’t work without a new TPS to voltage map. The idle adjustment is very sensitive to changes of only 0.02V or so. To make this change requires knowing the original TPS voltage at idle and full throttle and adjusting the map to ensure the new TPS gives the same voltage at those positions. It isn’t just a mechanical change unless the voltages match exactly and requires Easimap to change.

The original was a jenvey I think he said. I have jenvey throttle bodies, apparently it was changed for an after market one they use as the jenvey's often fail.  He troubleshooted the issue via the ecu so i would have thought it was checked after the new one was installed. Sounds like it's best i spend another day travelling down there again..

[aerobod - near CYYC]

15 minutes ago, Ant2 said:

The original was a jenvey I think he said. I have jenvey throttle bodies, apparently it was changed for an after market one they use as the jenvey's often fail.  He troubleshooted the issue via the ecu so i would have thought it was checked after the new one was installed. Sounds like it's best i spend another day travelling down there again..

Jenvey don’t have their own TPS, but sell a number of different ones with the most common being the Colvern/Amp one, but have one from Variohm and contactless ones, too. The base idle voltage will be very dependent on how the car was mapped originally and dependent on individual preferences, as any voltage can be mapped to any throttle opening. With Jenveys SBD (for example) specify to set the voltage to 0.25V with clockwise opening of the throttle and the throttle screw fully unscrewed, then tighten the screw until the throttle opens with a voltage of 0.30V. Then full throttle voltage is determined and the throttle map scaled from idle voltage to full throttle voltage accordingly.

If they have moved the idle throttle stop in any way, a throttle body air flow balance should be done again to ensure all throttle bodies are giving the same flows at idle, this will be worth checking anyway to ensure it is correct.

it is also worth going through this exercise for a new TPS even if the same as the original, due to manufacturing tolerances.

If the cold start fuel map was correct before, then it may be a question of just getting the TPS reference positions fixed, but if anything has been changed with the fuel maps, then a rolling road session may be needed to fix the mapping.

Edited May 18 by aerobod - near CYYC

[Ant2]

5 hours ago, aerobod - near CYYC said:

Jenvey don’t have their own TPS, but sell a number of different ones with the most common being the Colvern/Amp one, but have one from Variohm and contactless ones, too. The base idle voltage will be very dependent on how the car was mapped originally and dependent on individual preferences, as any voltage can be mapped to any throttle opening. With Jenveys SBD (for example) specify to set the voltage to 0.25V with clockwise opening of the throttle and the throttle screw fully unscrewed, then tighten the screw until the throttle opens with a voltage of 0.30V. Then full throttle voltage is determined and the throttle map scaled from idle voltage to full throttle voltage accordingly.

If they have moved the idle throttle stop in any way, a throttle body air flow balance should be done again to ensure all throttle bodies are giving the same flows at idle, this will be worth checking anyway to ensure it is correct.

it is also worth going through this exercise for a new TPS even if the same as the original, due to manufacturing tolerances.

If the cold start fuel map was correct before, then it may be a question of just getting the TPS reference positions fixed, but if anything has been changed with the fuel maps, then a rolling road session may be needed to fix the mapping.

Thanks for all the info. Seems like at minimum there is quite a bit of experience involved in setting these up (along with all the software and cable etc) and something I won't be touching, therefore another day spent on the m25 and at the garage again.