wierd engine problem

I have a 89 RS with the 305 and a 5 spd manual... Sometimes when im driving my check engine light flashes and the car starts to hesitate and shake(feels like you are tapping the gas pedal). I ran the car for codes with our diagnostic machine and it doesn't show anything. I replaced the cap and rotor, plugs, plug wires, and the O2 sensor but it still does it.

It only does this though after I've been driving for like 5 or 10 minutes but other times it won't do it at all.

i cant help much but id recommend a new air and fuel filter. it did wonders to my car. try getting sum codes off of it again. i would think sumthing would show up if the ses light is on. good luck.

alright...i'll try the air filter, i already did the fuel filter...forgot to mention it before...but i'll try the air filter and i'll let you know what happens

Are you sure there are no codes? I've never used a tester on an OBDI, but I have checked many for codes. They usually store a code whether the light is on constantly or intermittently.

Are you sure there are no codes? I've never used a tester on an OBDI, but I have checked many for codes. They usually store a code whether the light is on constantly or intermittently.
thats what i wa sthinking, because my 32(egr) code doesnt always throw the ses light and the code will show up even with the light not on. and i think the air filter will help but u really need to get a code, so it'll pinpoint what it is.

I hooked the car up to an actual diagnostics machine/scanner, im not just trying to flash the codes so i know that it's not giving me any codes

maybe something's wrong with the ecm?

i replaced the air filter...no luck, same problem

yeah the air filter isn't gonna fix it. If it only does it after it's warmed up, the problem is happening when the ECM is in closed loop- working of the O2 sensor. I don't know what it is, but it could be a different sensor. I'm guessing you got a TBI- it could be a intermitent fuel pump problem- rig up a T fitting on the fuel line before it goes in the throttle body and check your pressure. It should be in the 9-13 psi range. Obviously if its a intermittent problem it will probably read fine until your driving and it does it, which would be harder to check fuel pressure while driving... hope this helps a little

thanks a lot...i'll try it out and i will let ya know what happens