'94 Plymouth Acclaim - 56k miles - 2.5 liter w/ 3 speed automatic tranny & A/C. Car is in good shape and regularly maintained. Here's the problem - I start it and everything is OK. I drive along at highway speeds (55 + mph) and everything is OK. Then I begin to slow down and as soon as I slow to 45 mph the "check engine" light comes on. Doesn't seem to be related to engine rpm's (as I put it in neutral at 60 mph and let the engine fall to idle with no light). A code 13 is then stored. I know this is a MAP sensor related code. My buddy (fleet mechanic for utility company) gave me a new MAP sensor to try. I clear the code and the same thing happens (always the exact same 45 mph). I've checked the vacuum lines and associated wiring and they all check out good.
Why the re-appearing Code 13 ? What am I missing ?
Thanks in advance .........