[G50] Hesitation between 1000 - 1500 RPM when cold

[hk20000]

My 1996 Q45t seems to buck and hesitate between 1000-1500 RPM when the engine is below optimal operating temperature.

The symptom goes away once the car is warmed up fully.

Did anyone experience the same and know the cause to this buckling problem? 1996 G50 Q45t with OBD2 ECU. Manual swap done with these codes constantly popping up : P0600 -> TCM control malfunction P1336 -> crank angle sensor installed but pointing somewhere just off the gears of the flywheel so it's "erratic".

I tried to replace the coolant temp sensor right in the front side of the engine but no socket can fit into that tight spot...I don't want to remove intake plenum in order to do that....Is there any other methods/tools you reckon I could use to try and replace the ECU coolant temp sensor? (located just behind the fuel line bridge between the banks and in front of the plenum) no 19mm socket is long enough yet short enough to go in there and turn the sensor out...

But that's my speculation anyway what's the really likely reason for the car to buckle at 1000-1500RPM ONLY and nowhere else?

[black g50]

I brought that sensor today.And I cant see how to change it,couldn't even get a finger in to undue the connector.Now your talking about the one right in front,not the one deep under plennum?

[hk20000]

In the 1996 version the one under the plenum is the one for the gauges (I unplugged the one in front and the gauges still showed temp, while OBD2 threw code for coolant temperature sensor) so it's the one nearer the timing chain for the ECU.

It doesn't seem to be the culprit though, as I unplugged that and drove the car it bucked just the same.

My BMW friend suggested that for some BMWs at start there's a 1-min cycle where the ECU just runs extra rich.... that could cause my bucking and I should look into replacing my sparkplugs (mine are copper ones done a year ago with a lowered heat range)

[black g50]

Bucking is from messed up fuel air ratio,or failing sensor.I have replaced everything that was suggested on here.Cant use cruise control cause shell start breaking up.Thought about plugs,only 5years old less than 10000m on em.My Rodeo just ate a plug electrode causing miss fire but it doesn't feel like that in the Q.

[Infinitiguy19]

Crows foot flare wrench with a bunch of U joints may work.

[hk20000]

As far as I can work out the symptom happens at the first minute of starting and goes away regardless if the engine is warm or not. Then 100% of the time its goes away. I'm leaning towards a dirty maf and it works in a crappy environment so it needs time to get warm enough to get around the crud and measure actual air flow.

[black g50]

Where is the cps located?I found a sneaky oil leak back behind engine,hope it's not there.

[hk20000]

CPS is in the rear of the engine sitting on the transmission. It isn't sealing in fluids though it's a hall effect sensor pointing at the flex plate for an auto and a flywheel for a manual swap.

Doesn't seem to do anything other than throwing codes. The car seems to drive just the same as long as it's somewhat connected.

[black g50]

Any change in running condition?

[hk20000]

I added a ground strap to the head And it seems to have made the symptom lesser but its still there

[hk20000]

Back to the topic.

Now I have a better understanding of the issue. This is the very specific condition at which this will occur:

1. the symptom does NOT occur if it's parked overnight and fully cooled down.
2. the symptom does NOT occur if it's only been restarted momentarily after a stall.
3. the symptom DOES occur if the car engine is stopped for anything between 2 minutes and 3 hours where the coolant temperature does not dip past the lowest point in the temp gauge.

What do you think?

[texasoil]

dirty/faulty throttle position switch

[hk20000]

As in throttle position sensor?

[black g50]

Mine was between MAF or thermo,not sure which one fixed it.

[hk20000]

I did a thermo only recently so I guess MAF?