Finished a Head rebuild, on my 1990 240, changed seals, etc. and on restart engine has a very rough sometimes stall in morning, cold rough idle. I adjusted the idle screw up to give to my son to start driving, and that overdid it, and now that it has warmed up, it has a very fast idle.

Head was milled to max ... cut down 0.020".

I am wondering if I did something I should not have, causing poor cold idle, like using teflon tape on the temperature sensors? or something.

I checked timing, and it is dead on, very smooth, I can tell I have more power.
Also changed transmission seals, kick down cable and filled with synthetic Dex VI.

I did not change any sensors.

Any suggestions...what to troubleshoot... start with temp sensor resistance? O2 sensor?
Thanks - Old Guy

1) The ECU controls the idle speed. The "idle screw" is for adjusting throttle plate position, not idle speed. It's now called the "throttle stop screw". See Bentley section 250 and the related parts of 241 and 242.

2) To control idle speed, the ECU needs to know the engine temp. That means no teflon tape on the Temp Sensor threads. They make the ground path for the two sensor elements (FI and Ignition). The sensor should seal with a copper crush washer.


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Bruce Young, '93 940-NA (current), 240s (one V8), 140s, 122s, since '63.

Thanks to posts on suggestions and info. I have adjusted the throttle butterfly back to its original position, and only gotten around to checking the engine temperature sensor... I think it is ok?

I have not checked the idle switch, the MAP, O2 sensor, or idle inject valve.

When I adjusted the throttle "butterfly" idle stop off the closed position and the engine warmed up to normal, the idle was way too high, and the engine raced in neutral.

I still need to get around to checking, but I have managed to step on throttle pedal until I get moving, and when the engine warms up it runs fine at idle.

Have been driving to work and busy to check further... will update as I get to checking.

Thanks - Oldguy

Other post referring to IACV is the first thing to check. Perhaps you replaced the valve backwards or did not get the electrical connection tight.

Next to check is the throttle position sensor, is it adjusted properly (see FAQs).

Check the electrical connections on all your sensors in the engine compartment including the Mass Air Sensor.

The "idle adjustment screw" you reset is only a throttle plate stop. It really is not for idle adjustment.

Did you clean the throttle body when you had the head off? Some crud may have stopped up the idle air ports when you were moving things around.
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1999 E320-200K 1994 F150 (awaiting a new engine) 1989 560 SL-180K 1994 945T (daughter's)-312K 1986 242Ti (awaiting a B230FT transplant) 1968 GT500KR (under slow restoration) 2007 HD Nightster (son's ride)

Check to see if the Idle Air Control Valve is working. It should be supplying the air at idle.

By adjusting the throttle stop screw, you are opening the throttle plate and feeding air through there instead. So when the car is warmed up, the throttle plate remains open too much.
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1980 245 Canadian B21A with SU carb, M46 trans, 3:31 dif, in Brampton, Ont.

Hi,

What exactly are you adjusting because a 90 240 with LH 2.4 doesn't have any idle adjustments? Did you swap the 90 240 fuel injection system to an earlier version?

Travis