1999 Honda Accord Idle Surge – Stall – Unstable Engine RPM

1999 Honda Accord Idle Surge – Stall – Unstable Engine RPM

Short and sweet but a real issue from a real shop. I apologize for the crummy cell phone photos. I left my camera at the office.

A used engine was installed in the vehicle. It started and ran fine. However, once off idle it would surge and stall. The engine RPM would flare and lope up and down. The shop stated when the TPS was tested (via scan tool) voltage did not fluctuate, it stayed steady. They swapped the old throttle body over to the new used engine and just about every other part on the engine.

I backprobed the TPS with my DVOM. While operating the trottle I monitored my DVOM and scan tool. What I noticed was voltage changed at the sensor but was steady at the scan tool. The big giveaway was the voltage was different. It was 2.35 on the DVOM and 0.25v on the scan tool.



I checked the ground and 5v reference, both were good.


I scrolled through the scanner and what I found next was no surprise. The MAP signal would fluctuate in sequence with the throttle being opened. This was performed KOEO, there is no change in MAP (normally) when engine is OFF.


TPS and MAP connectors were swapped during the engine install. I rerouted the wiring. Plugged the correct connectors intot he sensor and the vehicle was fixed.

Blue connector: TPS
Grey connector: MAP
All done in about 10 minutes. 5 of which was setting up my equipment. Every now and then we need an easy one.