97 Protege engine problems
 

Hi! I've got a '97 Protege (1.5l, 5spd, only 85k miles) which has a couple of issues. It only has 140psi compression on one of the cylinders (was told it might be the valves, and if so, there was nothing worth doing about it). It kind of lurches at low RPM, and will sometimes stall at idle, especially if the AC is on. Recently it needed a new Cat due to an exhaust leak right at the joint between the cat and pipe, and after that was done, the stalling and lurching got worse. Also, the throttle response just got bad after the cat job; If I give it a little bit of gas it does fine, but If I push the pedal down too far, the engine just idles as if I wasn't pressing the gas at all. But even before the cat, it would lurch a bit if you gave it too much gas at RPM below 2000. Last but not least, it's kicking out an engine code for the MAF sensor too.
Anyway, I wanted to put this out here for the experts in Mazda-land - any of your expertise would be much appreciated. I like the car and would like to see it run right, but I'm wondering what that would require. I'm guessing I may be looking at a new engine to really fix the compression/valve issue, but would just doing the MAF fix the throttle response issue?

mwcten,

What is the compression on the other 3 cylinders? Any other history concerning this issue to relate? 140 is somewhat low, but we need to know the condition of the other 3.

Did the MAF code pop up before or after the Cat work was done?

As far as your code, sometimes you can remove the MAF and carefully spray clean the sensor wires using a cleaner made specifically for this purpose. Start with that, have the code cleared and try it (if it were me, I would disconnect the battery for about 5 mins after the code is cleared to force the computer to relearn it and the other sensors performance). That MAF sensor is very important as it tells your engine computer how much air is being ingested by the engine which affects spark timing, fuel injector duration, etc. Dirty/contaminated sensor wires in the MAF can cause the some of the driveability issues you describe.

Start with the easy stuff and we'll go from there...

J

Replaced the MAF
 

I bit the bullet and had my shop replace the MAF sensor and was pleasantly surprised - $230 later that seemed to fix all of the problems, even the low-RPM lurching I've endured for the entire year that I've owned the car. They cleaned the old MAF out when they replaced the Cat a week ago, and I suspect they screwed it up when they did that, although being the factory sensor it was probably due to go. The compression issue doesn't seem to be a driveability problem at all - the one cylinder was 140psi, the other three are 170-180 last I checked, but still, I would say that it drives like new.
My last issue is to see if my milage improves after this; I've always got 30-31mpg out of the car which I've always considered very low, so with my next tank I'll see if that improves.

With an engine this old you could do a "SeaFoam" treatment. It burns off deposits and has the ability to get piston rings unstuck. A stuck ring could be a cause for lower compression. Go to an industrial area to do this. You will make a huge white cloud....