Car hesitates between 2500-2800 rpm

[max_ae86]

I'm facing a strange problem for a while. The engine hesitates around 2600 rpm, particularly when it is still cold. After it gets warm, the problem almost disappear. I've tried a lot of things but can't fix it It is 4age AFM engine. Plugs and cables are new, TPS set correctly, can't see any air leaks, throttle rebuild... Any suggestions?

[Apsogos]

do you hammer her when is cold?

[max_ae86]

Apsogos Wrote:do you hammer her when is cold?

No, of course not! Just normal ride but even then it struggles around 2500-2800. If I hit the throttle pedal to the floor it almost stalls. When it gets warm the problem almost disappear, I can feel just a little lack of torque around 2600 rpm.

[Bean]

sounds a bit like the auxiliary air supply or your cold start injector is playing up (as far as I remember the cold start injector is on a timer and not based on an actual temp reading).

[jondee86]

Checked your ignition timing recently ?

Cheers... jondee86

[jonis79]

I had same problem with AFM. When I changed to MAP (changed ECU and distributor), problem gone. I will suggest you to change distributor, because problem is from 2500 to 2800 on all gears regardless of the load. ECU calculaiting RPM only from triger wheel in distributor, you can check signal with oscilloscope.

[max_ae86]

1) Auxiliary air supply working properly.
2) Cold start injector is normally active just few seconds during start up so it shouldn't be a cause.
3) I was playing with timing recently but also without success.
4) I will try to replace the rotor (I have one in spare) – this sounds interesting. I guess that it should be something with electricity.

[totta Crolla]

Sounds like the engine is going lean at that rpm point and at around that
temperature so it could be your temperature sensor.

Have you tried doing the diagnostic test ?

[ZDoman]

if the EGR system is not working, and your air intake or exhaust system is not original then its a common thing on AFM engines, because the EGR is recirculating some unburtn exhaust gases at this point, which can occur in lean mixture when not-working..

[max_ae86]

totta Crolla Wrote:Sounds like the engine is going lean at that rpm point and at around that
temperature so it could be your temperature sensor.

Have you tried doing the diagnostic test ?

Temperature sensor checked and working as specified. I have also checked groundings and found AFM housing not grounded (it gives 200 k ohm resistance). I don't know if the AFM housing needs to be grounded or not?