Rough running m50tu

[Hypr5]

Hey guys,

My m20 and m52 engines feel silky smooth, but the m50tu is getting a little rough. But what is bothersome is that the idle is pretty smooth, it just feels like every now and then it gets a little lumpy - not too big of a deal. Cruising / highway cruising is also smooth as can be, however acceleration is a little bit rougher (to be expected) - but high rpm (4k and above) feels like an old, tired 4 cylinder - it just sounds like its straining and it vibrates very strong. My m20 and m52 are just silky smooth above 4k rpm and if I give it gas, they pull nicely... not this one. It's annoying when I want to pass on the highway and it just vibrates.

Any ideas as to what this could be?

[KenB]

Fuel delivery problem would be my first guess. Clogged fuel filter, dirty or clogged injectors, weak fuel pump, uneven pressure? Might be ignition related but I think fuel first...my 2 cents worth.

[Kalevera]

Need to know a bit more info on this to say anything conclusive. Fuel delivery is a good place to start. It seems like we spend a lot of time fixing secondary air system and vacuum hose leaks on the M52/tus. The OEM conti hoses have a tendency to turn into silly putty. The secondary air valve and hoses get clogged and crack. Not necessarily anything associated with a service engine soon light, but symptoms can include weird noises on cold startup, weird noises at idle, bad idle, you name it.

Then there's the vanos issues. I'll leave it to others to describe them.

best, whit