After driving home from work with no issues for 35 miles at 65mph I get to the stoplight at the bottom of the exit ramp. For the last two miles home, at 35mph to 45mph, I have engine trouble. It’s exactly like someone giving it gas, then letting off the gas, then giving it gas. Id say it cycles in 2 second intervals. The issue also occurs on cruise control. The next day I start the car and it is fine. The next night, same story on the drive home.

A mechanic friend was certain it was the purge valve. I changed that out because it was super easy and inexpensive. I still have the issue. I've since been able to get the engine codes. They are P0123, P0421, P1102, P1123. Also, for full disclosure, the Valve Cover Gasket is leaked badly. I'll be replacing that this weekend. I'm wondering if enough oil has leaked out that it has fouled another component.

Has anyone experienced this before and did you find a solution?

Thank you in advance.

 

The codes P0123, P1102, P1123 all relate to throttle position switch or wiring. The orange wire at the TPS should show ground (you can splice in an extra ground to verify).

The code P0421 relates to catalytic converter efficiency. Need to do some diagnosis with a real scan tool to verify but the normal issue is "bad cat".

Fix, replace the TPS, clear the codes and drive it.

Your lack of power is most likely a defective TPS, once it finally gets hot it flakes out.

 

Another thing worth checking is the ECM grounds. Verify they are clean and tight. Actually remove them for the inspection.

All ways list year, model, mods when asking a question. We are lazy and do not want to dig into your profile to know you have a 99 NB.

The cat code MAY have been caused by the TPS freaking the ECM out. Don't worry about it until it constantly returns after clearing. This code (if the cat is really bad) will return after 30-60 min driving.

You also need the ability to clear the codes. Diagnosis is pull codes, clear codes, drive car, as soon as the light comes back on pull codes. Commonly the first code that returns is the root issue.