1.3L EFI surges on steady throttle

[Jules]

1.3L EFI 1990 Samurai engine in buggy.

Recent history: flopped it 2 times wheeling in the bush and ran it low on oil. Found oil in air filter after checking out the vehicle at home, so I assume oil may have plugged something else up.

Idle is fine. No problems.

If I give it steady throttle above 2000rpm it will surge and is worse at full throttle. I've tried disconnecting the ISC and this only reduces the idle speed but doesn't seem to affect the throttle surge. Problems occurs with cold and warm/hot engine. Haynes manual only says vacuum leak and fuel pump for potential problems. I have replaced the fuel pump. I've tried some newbie vacuum leak tests with starter fluid, but I'm not sure my testing is reliable. I may get a smoke machine and try that.

Videos below:

This one shows gauge cluster while surging.
https://www.youtube.com/watch?v=DT4lP-N-C-4

This one below shows throttle body while surging. Looks like it's too much fuel?



Extra videos:
https://www.youtube.com/channel/UCjpmajB...yQySjr_zWg

[fixkick]

1.3L EFI 1990 Samurai engine in buggy.

Recent history: flopped it 2 times wheeling in the bush and ran it low on oil. Found oil in air filter after checking out the vehicle at home, so I assume oil may have plugged something else up.

Idle is fine. No problems.

If I give it steady throttle above 2000rpm it will surge and is worse at full throttle. I've tried disconnecting the ISC and this only reduces the idle speed but doesn't seem to affect the throttle surge. Problems occurs with cold and warm/hot engine. Haynes manual only says vacuum leak and fuel pump for potential problems.  I have replaced the fuel pump. I've tried some newbie vacuum leak tests with starter fluid, but I'm not sure my testing is reliable. I may get a smoke machine and try that.

Videos below:

This one shows gauge cluster while surging.
https://www.youtube.com/watch?v=DT4lP-N-C-4

This one below shows throttle body while surging. Looks like it's too much fuel?



Extra videos:
https://www.youtube.com/channel/UCjpmajB...yQySjr_zWg

wow that is a nasty surge,  ISC wires not connect leaves out that the the ECU surge if idle switch sticks closed, off idle.

is that dash pot, device just to rear of fuel line and is that DP rod moving?, and bumping the idle stop?
if not its a very bad vacuum leaks (even the brake booster can cause very odd vacuum leaks.
pinch hoses, plug some.
some demon there, may take lots of deep looking to find where that extra air is common from.

and sure fuel pressure must hold steady on this TBI (use filter test port) on 8v,  unlike the complex 16v fuel pressure does not change, only by altitude.

[Jules]

Thank you. I will do a better vacuum check.