92 Civic CX Hatch Endless TPS woes

Maintenance/Repairs
1

Hi guys! I have a 92 Honda CX hatchback, 5pd with 140k on it. Since I bought the car used about a year ago it’s had a low speed stumbling/bucking issue. For the most part, it’s only when driving slow and steady but occasionally at highway speeds it’ll do it as well. It’s as though the whole engine just cuts out for a second. Giving it more gas always brings it back but it’s incredibly annoying, especially in a parking lot with a cup of coffee or something in your hand.

For starters, the rotor, wires and cap are all very recent. I pulled the ECU codes and it indicated #7, Throttle Angle Sensor. Bought a new one, calibrated it, reset ECU and drove on. No change. Car still bucks and the CEL comes on occasionally. At first, I suspected the plug to the TPS since it was loose. I pulled new wire and soldered directly to the ECU and TPS. No change. Of interesting note, when the CEL would come on, it seems the TPS falls offline and the car runs great! I disconnected it for a tankful and noticed my 40mpg/hwy go down to 25mpg. Completely unacceptable for a car so painfully slow.

Another observation, the stumbling doesn’t start until the car warms up. Also, if it’s particularly humid/raining, sometimes it won’t do it at all. A lot of people have suggested the O2 sensor, distributor, fuel pump/filter. I don’t have money to just start throwing at this thing and of many similar issues I’ve read of others with the same car, nobody seems to have a solid fix.

I’ve replaced the TPS, completely cleaned the throttle body and IACV, checked for vacuum leaks and even opened up the ECU looking for cold solder joints. It looks newer than new inside.

Like I said, with the TPS disconnected, car runs great but the mileage goes south.

Thanks everyone! Great forum!

John
Tacoma, WA

2

I’m not sure what the resistance of a TPS on a 92 should be but it is still a potentiometer. On one of the connections to the TPS, you should see ground. On another you should see some steady voltage. On later accords, that’s about 4-5 volt but could be different on yours.
The third connection is the runner, varying the voltage in direct proportion to the throttle position.

I’d measure that voltage and see if that’s indeed happening.

3

I too would wonder whether or not you’ve actually put a meter on it to check. As mostly described by RemcoW you should find one wire that gets a constant voltage at about 4.5V or so. The other wires is the signal back to the PCM. Its probably supposed to be something like .5V at closed throttle and should increase very gradually as the throttle is opened - up to something around the reference voltage at WOT.

Those figures are just typical - so it could be different for this car.

4

A low speed stumble at idle that occurs once the engine is warmed up immediately makes me think there is an EGR issue, regardless of any codes that are present. Just for kicks, try disconnecting and plugging the vacuum supply line on the EGR valve and driving the car. Needless to say, this will set another code, but if the issue goes away, it means the EGR valve is staying open when it should not be, like after you have released the accelerator. If this is the case, it could be the EGR valve itself or a solenoid/modulator that actuates the valve, more likely the latter. I don’t know exactly how the EGR system works on this car, but this is what the symptoms sound like to me.