1.9 L starts just fine but will not keep running at idle. Stalls when coming to a stop (automatic). Just changed oil, didn't help. If I hold the idler arm just a tiny bit, runs just fine. Please...
With carbureted cars, the idle speed was set by adjusting a small screw that held the throttle open just a little. That screw rested on a sort of a disc with graduated steps on it, the fast idle cam. When the choke was partially or fully closed, that disc was turned a bit to present a higher step for that throttle-adjusting screw to rest on, providing a higher idle speed during warm-up.
With fuel injection, there is no choke, and the throttle blade almost completely closes at all temperatures and states of warm-up. When the richer mixture is needed that a choke used to provide, the Electronic Control Unit (or Electronic
Module) simply flows more fuel through the injectors.
There also is a short (incha and a half, maybe?) air passage that opens onto either side of the throttle blade, a bypass passage. There is an electrically controlled valve in this passage.
When the engine is cold, the ECU opens that valve a little more to produce a faster idle, as the "fast idle cam" used to. When the air conditioner is turned on, presenting a load to the engine, that valve is electronically opened just a little to keep the idle speed the same even with the higher load. If the car has an automatic, when it is put into gear, that valve is opened a little to keep the engine running with the additional load the torque converter applies to the engine.
All of these idle-speed adjustments make use of a tachometer function in the ECU.
Now. These bypass air passages can become blocked, and the electrically operated valve (it is adjusted through a motor turning) can get enough accumulated crud on it to prevent its operation.
I would recommend first locating that bypass passage and its valve, disassemble that and clean everything carefully. Reassemble and see if all is well.
If not, I would think the ECU or its wiring is where the problem lies. Naturally, look for the connector that might have fallen off the bypass control valve, and so on.
The fact that the engine runs would seem to argue that the tachometer function and the accompanying circuitry are working correctly.
Aug 09, 2010 |
1999 Saturn SL