QuestionMark,
I have a 1989 Mercury Grand Marquis LS with the 302 V8. It has 258,000 miles. The car quickly within a month went from averaging 21 mpg to 15.7 mpg. At the same time the trans started to mess up and was rebuilt by AAMCO. Now when you let off of the gas pedal, it tend to go "ka- gunk- ka- gunk. I replaced the Throttle Position sensor with a Motorcraft part(the correct one). The technician at the dealership looked at the throttle body and said it was in great shape. It still does it, and gets poor gas mileage. I have also replaced the fuel filter, fuel lines, fuel pump relay, and has been kept up on all regular maintenance. The car also seems to run lean. I have a code reader, and it keeps running up code # 34, which stands for: EGR valve, and Exhaust Gas Recirculation System. I think part of it may be an O2 sensor, but it has officially stumped me now! If you do figure something out, could you rate it on a scale of 1-10, 10 being 95- 100% sure. Thank you for at least reading this, and good luck.
Answeri appreciate all the info you gave me that means a lot when trying to help someone-
on the 89 egr system you will have and egr valve/vent control solenoid/evp sensor and passages in throttle bore-the most common thing is an evp sensor but anything and i repeat anything you get a code for needs to be diagnosed anything else is just a guess and when you throw parts at a car for a problem unless you get lucky the first couple of times you usually waste money-
as far as gas mileage goes the number one thing this time of year is most people let cars warm up before they take off which is ok i do that to but if you do that 5 minutes a day you'll shave over 30 miles off of a tank of gas-a thermostat opening two quick or stay open will kill gas mileage because your vehicle does not have a choke it depends on coolant tempature-when it is cold the coolant temp sends cold reading to ecm and it keeps injectors open longer to make car run better and as it warms up injector on time gets shorter.
a vacuum leak under upper intake or at rear of engine will show lean and computor will react by richening mixture.
as far as clunk on transmission first undo egr valve and roadtest if it doesn't do it then probably and egr vent solenoid-if it still does it i would get a second opinion but would bet transmission case is worn out in rear.
i can't honestly rate 1-10 because to many variables. good luck though.
