Hello,

I have a 1988 244 with 234k in the odometer and tuned it up beacuse the valves were chattering under load. After tuning it up I have a few questions regarding the idle specs and timing. The throttle body idle screw was 2 turns in and the black idle screw was about 2 turns out as well. After hooking up a tach I found the idle to be at 1100 rpm. I turned both idle screws all the way in and this lowered the idle to 800. I then checked the timing.

The timing was way out (30+), so I turned it down as far as I could. This did not get me to the 10-14 degree range but was closer. I then drove it and it had very little power but did not clatter the valves.

My questions are:

1. What should the black screw be set at?

2. Has anyone had a similar problem?

I have adjusted the timing to where it is nearly acceptable, but according to the pointer it is way off. I am going to start by verifying the mark on the crank pulley is actually TDC and go from there. Thanks in advance for any help.

The idle speed is controlled electronically by the idle air valve which bypasses air around the throttle body. Idle is not controlled by the buttterfly being kept open slightly as on older carberators. Final idle speed is not adjustable and should be at 750rpm and 900rpm when AC is on. The screw is adjusted so that the linkage does not put a load on the throttle butterfly or it's shaft. Back off the screw then turn in until it just contacts the lever then turn an additional 1/4 to 1/2 turn, check throttle position switch to click closed when throttle closes and click open when throttle just starts to open. Black knob adjusts base idle by bypassing air internally in the throttle body around the closed butterfly. Set for 650 to 700 with idle air control disabled by grounding the blue white wire in the test connector near the coil. Disconnect the grounding jumper, now if the idle air control valve system is working your idle speed will jump up to 750rpm.

Of course for all this to work your throttle body inards should be clean and free of deposits which may interfere with the butterfly movement.

I believe all of the above is decribed in the 700/900 FAQ section which will be the same for your car.

Forgot this in my post above.

timing should never change on this engine unless the distributuer is disturbed. Yes you are wise to check that the timing mark corresponds to TDC as the harmonic balancer bonding rubber can slip. Happened to me.

Not sure what you mean by valve clatter, tune up will not get rid of this nor will timing.