Surging at 2000 rpm... 740 GLE, 1990.

djzuelke · Post by **djzuelke** » 26 Aug 2009, 13:14

Just finished putting together the top end of the engine after a broken belt. Starts and idles well but has some driveability problems. Can rev the engine (in neutral) up to about 2000 rpm but it surges at that speed. Will not surge at 3000 rpm but when the accelerator is released just a bit, the tach immediately falls to 1500 and surging starts again. Have checked and rechecked vaccum lines and grounds. Haynes manual says that it is necessary to drive the vehicle at least 10 miles to allow the ECU to relearn the correct factors. Is this in fact true?

Post by **billofdurham** » 26 Aug 2009, 15:28

The computer does need to relearn but it may take more than 10 miles.

This is the Volvo instruction to dealers:

740 computer relearn.pdf: (738.04 KiB) Downloaded 184 times

Bill.

djzuelke · Post by **djzuelke** » 26 Aug 2009, 20:20

Thank you Bill. Will try the technique suggested by Volvo and let you know what happens.

djzuelke · Post by **djzuelke** » 28 Aug 2009, 19:11

Volvo computer relearning procedures did not seem to have much effect on my surging problem. Alas... On the road it does some strange things. Starts and idles good but when accelerator is pressed down surging will start, usually between 1500 - 2000 rpm. However, when pressed down to passing gear, it will accelerate and run well at 60+ mph. Slow down to 55 and the tach will suddenly drop to 1200 rpm and surging will commence. Will also run normally at 40 -45 mph - usually. Am thinking the TPS might have a bad spot.....

djzuelke · Post by **djzuelke** » 09 Sep 2009, 21:04

Surging continued..... I replaced the Throttle switch and Mass Air Flow Sensor. Still have the same problem. What would cause the tach needle to suddenly drop significantly while reducing throttle pressure slightly? My next step is to swap out the Ignition Control Computer since it appears that the tach is plugged into it.

Some time ago, I had an innermittant problem with complete lack of acceleration mostly when cold. Would have to pull over to the side of the road and let the engine idle for a few minutes and then it would behave normally. Eventually, that problem cured itself. Wonder if it is related to the current surging problem?