intermittent 2.8 mpfi problem

I have a 85 cam. with a 2.8 mpfi with about 90,000 miles on it. I replaced the timing chain/gears this last summer and when I started it back up it sounded like the valves were going to come out of it. So I tore into it again and every thing was lined up right. Started it up again and the same thing. After it idled for about 5 miutes it sounded like it was suppose to and ran fine. The thing never idled properly before working on it (wanting to die). Now after 7 months of driving it, it will start missing and it sounds like collapsed lifters and knocking. It doesn't do it all the time or at different rpm's or under certain loads, hot/cold. Then all of a sudden it will run fine. The problem is very intermittent. Could the engine timming from the computer do this? Also about the crappy idling, I adjusted the tps voltage according to the book and still have the idling problem. Changed fuel filter and checked fuel pressure. No improper codes show up. Any ideas what the problem could be???

Thanks

Welcome to the club. I am working on a similar car. It's an 86 spt coupe with the same 2.8L MPI engine.

My beast was inherited from my kids. I have used it on and off for several years. I was planning on doing something dramatic under the hood before using it again but I need it for transportation for now. As a result I pulled it out of the garage and tried to doctor it up. The doctoring on something this old isn't as easy as I thought it would be. It has more problems than you want to know about right now. The shame of it is that it runs great. It idles a little strangely and won't pass NJ emissions inspection. Other than that I could comfortably drive it cross country.

The noises in your car, it's really hard to give a decent opinion without hearing it. Sure sounds like a lifter gone wild. If it isn't I'd be worried about oil pressure. On the other hand is it possible the thing is just running that badly intermittantly? A bad enough misfire could make it sound pretty awful. I guess that's what you are thinking given your questioning the engine timing. The crazy thing with intermittants is that it could be a lot of causes. An worn wire grounding now and then could cause crazy stuff.

As far as the idle--One of the better pieces of advice I/ve gotten in trying to fix mine is that if it runs well but idles poorly look for vacuum leaks. On mine I found a pile of them. I may have finally found the last one yesterday. It was that crazy fitting near the distributor on top of the block. It picks up engine vacuum and distributes it to four lines running to emissions controls. A really crazy arrangement. I wanted to replace it all but so far I haven't found a decent source. There are a lot of plastic parts involved. In any case I think I plugged the last leak. Notice the "I think." I spotted the leaks using propane. If you are not familiar with this stunt be careful or the car could be the least of the problem. Propane and the human body burn very nicely:)

The emissions system on this car is just complex enough to make your life miserable without being really as effective at announcing what's wrong with the car. I went through the same thing with the tps, played with everything I could and wound up picking up a scan tool to diagnose the problems. The jury is still out. As of right now mine has an intermittant code 24 (vehicle speed sensor). That one makes sense. What is not making sense is the scanner thinks the car has an automatic trans. It has a 5 speed. So, among other things, I am trying to find out what the actual PROM Code should be for this car. It could be it has the wrong PROM or the scanner is going beserk.

All in all I plan on trying to get mine through inspection then see what I want to do with it. I think a couple more days of work should get it ready. On the other hand, if I could do it again from the getgo, I would pull the engine and reseal everything before playing with the car. There are just too many things that are too well broken in.

Anyway, I post this including my experiences for whatever its worth. Good luck to both of us.

my bro had a 86 firebird with the 2.8 muti port, his done the same thing. he replaced almost everything on it and no improvement. so i got a new mass air flo sensor and replaced that and it fixed it. have you checked yours