Hello, I have a '92 VX that hesitates badly once it warms up (runs fine when cold). I purchased this car recently, the hesitation was pre-existing. We have done a full tune up, including plugs and wires, fuel filter, air filter, oil filter, oil etc... This didn't help.
I have a spare engine which we have used to swap out sensors and parts. We have swapped out all the sensors on the intake manifold, the distributor, and the ECU, none of this has helped.
The check engine light has never come on, so there are no codes to help diagnose.
It has a 5 wire O2 sensor, which looks newer, I have not confirmed whether it is an NGK or otherwise (have read that Bosch can be problematic). Any help or suggestions on how to correct this problem would be appreciated

 

Maybe there is a vacuum leak some were or a vacuum hose is not installed in the correct form. Possible bad EGR vavle or the EGR vavle hose's are not hooked up properly. There should be a picture under the hood like a diagram for the correct pattern on how to hook up the vacuum hose's.

 

The lean burn engine was tuned to the ragged edge for maximum mpg and so it's very prone to hesitations. Enough so that it got knocked down a few points for reliability compared to all the other trim Civics in their long term reviews.

I suggest you take off your intake manifold and throttle body, clean them out completely, replace the gaskets and all the vacuum lines.

Make sure you have the right spark plugs. Parts stores will give you DX, LX, EX plugs for a VX but they're the wrong part. The correct part number is on your timing belt cover.

Check your base ignition timing.

O2 sensor is absolutely critical on this motor. But being that they are very expensive, you should test it with a multimeter to verify it's bad before you replace it. Your ECU wont throw a code for the O2 sensor unless it's a catastrophic failure. But O2 sensors can go bad long before they throw a code.

gassavers.org is the site for VX owners.

 

Thanks for the information, we will give your suggestions a try and report back. I have also posted the same question on gassavers.org, thanks for the suggestion.