engine surge

[jdtuck13716]

i have 1990 300zx, non turbo, 135,000 miles. the problem is engine surges at highway speeds between 300 and 1,000 RPM. recently tuned, trans fulid changed, air filters changed. does not happen when not in overdrive.
any ideas?

[300ZXttZMAN]

Welcome to NICO!

Interesting issue. I"ll move it to the Z32 tech section hopefully someone will be able to lend a hand.

[t.mcginley.jr]

surging while cruising has been associated with bad O2 sensors, even if the ecu isn't throwing an O2 sensor code. They aren't too expensive, try swapping in new ones

[jdtuck13716]

thank you

[300ZXttZMAN]

[GerryO]

A new TPS might be even less expensive than a new O2 sensor, and cleaning the MAF would also be a good thing and is easy to do.

A dirty MAF in my '97 F150 was responsible for slight stumbling at shift points and pretty violent bucking in OD at freeway speeds. Lighter pressure on the throttle made things worse.

An out of adjustment or worn TPS will cause transmission "hunting" at cruising speeds.

A failing O2 sensor in my J30 caused the exhaust to smell a bit different and the CEL to come ON, when slowing down at the very end of long drives. If your O2 sensors are original though, they probably are due.

[jdtuck13716]

thanks very much- i will pass this along to my mechanic and hopefully be able to solve this issue that has been very frustrating!