Hello all, as the title indicates this is my first post and i own a 1990 volvo 740 with an intermittent acceleration problem. I bought the vehicle off of a friend recently for $300. according to him the problem was fixed temporarily once and the mechanic thought it originated from the gasket on the feed to the turbo that confuses a sensor. im not a car guy but i would think that replacing a gasket wouldnt be a temporary fix. the problem only crops up every couple of weeks and results in the car accelerating slowly and refusing to go above around 20mph. any help or advice would be greatly appreciated!

 

Hard to diagnose a problem that only happens every couple of weeks! Sounds like a MAFS issue but this is just a guess; the other things you mention don't make much sense. Wait and see if it gets worse, and then...

 

I figured itd be a long shot to diagnose with the limited info i have. Would starting off replacing oil lines and air hoses be a dumb place to start?

 

If the knock sensor is detecting any pinging or detonation that's what it's suppose to do. It's called "limp" mode, to get you home. My car did it but it wasn't pinging, it was a bad knock sensor. I replaced it and haven't had a problem since. One thing to be careful of is over tightening it. That can distort the connection to the block. You might try removing it and lightly sand the sensor(it has a smooth, brass surface where it mounts) and the block. Remount it and try again.

 

yes.

oil lines, I would only replace on evidence of oil leakagage from said line.

'air lines', you mean vacuum hoses? leaky vacuum hoses can be visually detected, they will be cracked. obviously, if you have hoses with cracked/split ends, yes, replace. other vacuum leaks can be detected via a 'smoke test' where you flood the area with an inert gas (co2 or whatever), and listen for changes in the idle speed.

 

Replacing parts *****-nilly is a an expensive proposition which almost never brings the desired result. In most cases it creates more problems than it solves...

 

probably limp mode caused from yes mentioned already MAFS..What happens is the foam insulation in the filter box breaks off in small pieces and because its plastic melts on the hot wire of the MAFS causeing it to go goofy and into limp mode because it cannot give out correct info to cpu. Take it out and carfully get some cleaner and wash the wire clean. Remove all the foam in the filter box used for noise deading by Volvo , father time killed it.
Hope this helps..