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Mpi Revs Hang For A Second Or Two


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#1 nickowen

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Posted 31 March 2020 - 04:06 PM

Please couldAttached File  181119F2-09BD-42A5-BCF4-117FA877CAA1.jpeg   32.95K   1 downloads

 

someone shed some light on a issue that I cannot seem to cure. 

 

I have a 1998 fully rebuilt, 1293cc Cooper sports pack with stage 3 head, 1.5 roller tip rockers, fuel pressure regulator, 52mm burlen metal throttle body, 3 branch manifold LCB, 3 inch fletcher exhaust and a k and n panel filter. Newly rebuilt gearbox with x pin diff and central oil pick up. 
 

My issue is that the revs hang for a second or two on overrun. It is really annoying as when you dip the clutch the revs do not drop instantly, so it feels like you are slipping the clutch slightly. 

 

Other than the above the car runs superbly with lots of power, no flat spots and very responsive. 
 

The spark plugs are relatively new and are quite black and sooty, except for the electrode being grey.

 

The mini has been put on a snap on reader and only came up with the usual faults that are not applicable to the mini. (Ambient air temp, and another that I can’t remember but I think it was an oil related fault that is not applicable)

 

The throttle cable is new and not sticking.

The throttle body is new and is not sticking.

Throttle pedal has full movement and the spring is returning it fully.

I have fully cleaned the IAC valve and renewed the o rings on the IAC and the plastic housing that attaches to the throttle body.

I have checked for air leaks but cannot find any and the pipe work is quite new (less than 3k miles)

 

The only way I can I stop the revs hanging is to disconnect the IAC valve, then the car runs perfectly except you have to give it a couple of revs when starting from cold as I have now disabled this feature.

 

Please could someone advise if the Rev hang is normal with the MPI or if not, advise what else I could check to cure this.

 

Thanks very Nick

Attached File  181119F2-09BD-42A5-BCF4-117FA877CAA1.jpeg   32.95K   1 downloads



#2 MacGyver

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Posted 31 March 2020 - 06:10 PM

Câble too tight? Mine did that and a tiny bit more slack cured it.
Might not be related to your problem but just a thaught.

#3 Quinlan minor

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Posted 31 March 2020 - 07:42 PM

I was all excited till I got to the bit where you'd fitted a new throttle cable. MacGyver's tip is worth a try, definitely.



#4 nickowen

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Posted 01 April 2020 - 06:58 PM

Definitely not throttle cable as I have disconnected and operated the butterfly.

 

Another thing I forgot to mention is that if you rev it hard, say past 3k the revs settle back quickly, but if you drive in a leisurely manner that is when the revs hang.

 

Also the revs do not hang if I disconnect the iac valve......

 

Do all MPI’s revs hang ??.



#5 MacGyver

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Posted 01 April 2020 - 07:05 PM

No, not mine. (two)
Can you get hold of a second valve?

#6 Quinlan minor

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Posted 01 April 2020 - 07:13 PM

My MPi doesn't.


Edited by Quinlan minor, 01 April 2020 - 07:15 PM.


#7 nickowen

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Posted 01 April 2020 - 07:13 PM

Do the revs hang on your MPI ?



#8 nickowen

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Posted 01 April 2020 - 07:20 PM

Ok. Thanks for your help gents.

 

I will order a new iac and let you know if it works.



#9 MacGyver

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Posted 01 April 2020 - 07:22 PM

Sounds like the valve has a malfunction, it seems to be over fueling a bit like when starting cold so could be the reason for the revs hanging.
If you could grab one from another mpi to be sure it would-be great,dont know how you could test it otherwise?
Minispares do there own apparently for 30 odd quid but do t know the quality of it. Genuine is about 60 I think.

#10 nickowen

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Posted 01 April 2020 - 07:37 PM

Ok I will replace it and let you know. 
 

thanks for your help.



#11 nickowen

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Posted 01 April 2020 - 07:56 PM

Order placed should be here by mon/tue next week.



#12 nickowen

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Posted 07 April 2020 - 06:25 PM

New IAC fitted today, but no change. 
 

Next purchase this week will be a Pscan cable to connect the mini up to my laptop and try and teach myself (hopefully with the help of you kind chaps) how to diagnose the issue.

 

What are you thoughts on Pscan over Arc4 ?...

 

Nick



#13 tmsmini

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Posted 08 April 2020 - 02:06 AM

If indeed you need to set the stepper or IAC valve, it looks like Pscan is read only and does not allow the setting of the stepper.

Features available:

  • Read error codes
  • Erase error codes
  • Live diagnostic data
  • Learn 5AS EMS code
  • Read 5AS input status

You may still be able to make adjustments and read where the stepper is.

It sounds like the stepper is out of range for the engine and cannot reduce the idle any further. With a new TB, this should not be the case.



#14 nickowen

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Posted 08 April 2020 - 04:40 AM

Thanks for the advice, I will give Pscan an email to check.

 

The revs do do hang if you give the car a bit of wheelie (rev it to over 3k), but if you drive it normally the revs hang. This is the bit that I cannot get my head round, as I would have thought that if the stepper needing setting it would hang all the time .?



#15 genpop

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Posted 08 April 2020 - 06:09 AM

Hi nickowen,

I know nothing about MPI`s, but could you possibly reset the ecu by disconnecting it from current (battery) by more than 24 hours?

Just a try.






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