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severe hesitation/bucking at low engine speed 700 1990

posted by  TBray on  Tue Jun 11 00:37 CST 2002
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What would be the most likely cause of severe bucking or surging at low engine speed? The problem only exists in the early phase of 1st, 2nd and 3rd gear. Toward the end of each gear, the surging subsides and above 30 mph, the problem disappears. No symptoms on the open road - no stalling or cutting out at stops or turns. Constant idle is maintained even during rapid deacceleration.

Thu Jun 6 16:13 MST 2002 post details work to date. I've also swapped the RSR and electric fan relay - cold start problem has lessened but I still have the 3-2-1 code of no signal to cold start injector valve. CSI is reading around 12 ohms at connector, wiring harness is okay to firewall. Should the ECU be sending this signal and if so, what other sensor input might be holding it off? RPM sensor, ECT sensor, MAP sensor?

I've cleaned and greased ground connections throughout the engine compartment. Once warm, car idles fine, runs fine - hot restart takes at least two cranks, but engages and maintains proper idle. It runs so well (except for the hesitation) after warming up, that I don't suspect the fuel pump - but it is the original pump with 170K miles on it.

Any ideas would be really appreciated. I may have to succumb to turning it over to a mechanic to finish the diagnosis as I'm down to just starting a parts replacement phase and I seem to be chasing my tail.

Tommy
'90 740 GL
B230F/Rex Regina/170K





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