Help with setting idle screw after I moved it

Sheila mentioned that the car was stalling at road endings, so tried the TPS reset, and that seemed to help. Took it out for a test drive and it was still doing it.
I took the IAC valve off and cleaned it. Replaced it and now the tickover was varying between 2000 and 200 revs and stalling. :nonod:


Disconnected the valve and the revs settled at 850, no problems.Now I've already tried a second hand one a couple of years ago , so looks like I need a NEW IACValve.

Got one coming from Brown and Gammons!

Changed the IACV today. The interesting thing is that the tickover was much faster with the new valve fitted but not plugged in. Running around 1000 rpm.
Using torque app, I adjusted the base idle on the set screw on the throttle body to 850rpm and then plugged in the new IACV. Reset the TPS and it all seems to be working properly now, finger crossed. :tada:

Hi David,

I have a slower than normal response from the engine RPM to decay down to idle speed, I have fitted a new IACV and re-set the TPS.

I have also fitted a new 'O'ring gasket to the inlet manifold and checked all the related vac pipes just in case I was drawing in air from somewhere.

It's an alloy throttle body but an ABS inlet manifold so not sure of the integrity and quality of a plastic over aluminium manifold or if this is a problem area on the 'K' series!

Just as a matter of interest on your Torque App what is reading for your TPS in the idle position? mine reads 3.9 at idle and 87.8 at full throttle, if its given as a percentage then I am only getting 83.9% of throttle.

My throttle butterfly is fully closed, however there is a small vernier adjustment on the TPS so I may see if I can adjust it down to zero and I will check that the butterfly is fully open when the throttle pedal is full pressed then re-set the TPS.

I'll have to go and check on those readings.
With the slow return to tickover, try disconnecting the iacv temporarily.

As a percentage I get 3.9% at idle. Wide open is 91.8%

Thanks David,

So the same idle value (3.9%) but you have a higher value for fully open position, I will check mine tomorrow to see if I can get more travel on the pedal possibly remove the underlay soundproofing under the pedal, will let you know also with the IAVC disconnected about throttle decay down to idle.

I would also check the quadrant on the throttle body for range of movement, and the the cable for slack.

Whatever low idle position you adjust the TPS at, after a reset the lower value is always 3.9%, no problem with the cable/quadrant, full opening is achieved; however after a reset the upper value is still at 87.8% (the TPS is a 4KΩ pot)

Just thinking about the fuel mapping and as I am unable to integrate the eeprom; the different upper values could be because I have the stepspeed version which has a restricted power output of 118bhp as opposed to the manual which is 134bhp which I think is done quite simply by the max RPM cut off.

The 134bhp manual variant limit is 6,800 RPM and the 118bhp stepspeed limit is 6,000; could have some bearing on the different upper values!

Anyway back to the problem of slow engine RPM decay down to idle; With the IAVC disconnected when the throttle is blipped the decay is still slow, the only difference is the RPM drops well below normal idle, nearly stalls then picks back up to idle then starts to hunt.

I think I am looking at a vacuum leak somewhere on the ABS inlet manifold; the consideration is dump the plastic one and fit an alloy version.

Anyone done this or have any info; i.e. if the last versions of the 1.8 MPI (none VVT) MGF will fit (same wiring plugs/sensors) or if the early versions of the 1.8 MPI (none VVT) MG TF had alloy manifolds?

I think your suggestion re Stepspeed and throttle opening is correct.
With the engine at working temp and the IACV disconnected I would not expect the tickover to dip below normal, so something amiss somewhere.

Have you tried adjusting the set screw up on the throttle body to prevent the dip in revs?

I got an alloy manifold from a TF135 and it was a straight swap.

I did the plastic for alloy (vvc??)inlet manifold swap on my 1998 f 1.8 mpi.
It was relatively easy except for the MAP sensor position. It was straight forward to seat the older MAP sensor in the gutted new style sensor at the other end of the manifold and extend the wiring.
all in all, just over a couple of hours work. :broon:

Hi David, I’m new to the forum and owning a 2001 mgf with 41k on the clock.
how would you go about setting the idle screw I cleaned the iavc earlier today as when the car went from high idle from cold to normal idle it would try to stall, I then tried adjusting the setting screw to bring the overall Revs up not knowing that the Ecu Would try to correct this by using the iavc unit to bring the revs back down.

I would just like to no what should I do to set the idle screw back up correctly.

Thank you so much

:welcome2:
Basically you need the engine good and warm, then disconnect the IACV. The idle should be stable at 850. If it isn't adjust the set screw to achieve 850.
Then plug the IACV back in and allow it to settle. It should now have an idle of 875.
Then you may have to complete a throttle position reset. That is ignition on, engine off, press the accelerator to the floor five times, wait 30 secs then turn the ignition off. Start the car and hopefully the idle is stable at 875.