Engine stumbling badly under load

Hi,

I am stumped with a problem with my engine - its a 1998 subaru impreza sport - EJ20 naturally aspirated.

Whenever i put the engine under load, for example driving up a steep hill, the engine stumbles badly and nearly cuts out.

I`ve been through all the basics - fuel supply is good, changed the plugs (twice!), changed ht leads.

There are no inlet manifold vacuum leaks or exhaust leaks as far as i can see.

The engine starts and idles fine and will pull away reasonably well. When i come to change gear, especially on a hill, when i go to put my foot down, the engine stumbles as if starved by fuel.

There are no error codes displayed. I`ve checked the throttle position sensor - this gives a reading of 0.5ohms closed and 4.5ohms wide open throttle. The air speed control valve looks ok and turns fine when i`ve inspected it. I`ve also replacd the MAF sensor with a replacement which made no difference.

If anyone has any ideas or suggestions, any help is appreciated!

cheers,
mike

Have you had a wideband O2 monitor on it to check what air fuel mixture is like in those conditions? It would let you know for sure what the symptoms are so that could help with finding a cure.

Have you checked the fuel pump, fuel filter?

Try asking on here as well. .:ImprezaSport.net:.

i haven`t had an o2 monitor on it as i`ve not got the facilities to do that at the moment - i`d have to take it to a garage to get that carried out. I`m trying a few different things before i take it there as i`ll probably have to get it flatbedded to a garage - don`t want to risk knackering the engine by driving it it if its not quite right or running lean.

i m picking up a new timing belt at lunch and will check tomorrow if the current one has slipped - this is about the only thing i haven`t looked at yet.

i fitted a new fuel filter and the fuel pump seems to be working fine. no blockages that i can see anywhere at the moment.

thanks for the link - i`ll put a post up there too.

cheer,s
mike