Engine stumbling

[TheStoot]

Hey everyone, just a quick question. I am going to change my plugs and wires soon but I have some engine revving issue. From an idle, if I stop the pedal down and rev it up (in neutral) the engine stumbles until i gets up past 2000rpm or so then it spins up great after that. If I slowly push the pedal down and let the rpm's climb slowly then there is no hesitation. I'm pretty sure my car is running rich because I still cannot get it to go into closed loop. Frequency valve doesn't buzz. Only does this at low rpm while driving also, once I get above 2-2.5krpm the engine is smooth as can be. Thoughts?

[Michael]

If it happened all of a sudden, check your vacuum lines. Have you recently been under the hood prior to this?

[TheStoot]

No it hasn't happened all of a sudden, it's been like this. I got to replace the original vacuum lines one of these days

[TheStoot]

There's no disconnected lines, but i can't imagine a small bad seal could cause this kind of noticable engine preformance decrease/hesitation?

[David T]

"Stomping" on the throttle and noticing hesitation in neutral is not a real test of anything. Do the tune-up. Check and if necessary change the air filter. Find and fix any vacuum leaks. Verify that all of the vacuum hoses are routed correctly, everything works, and no leaks. Check all of the throttle adjustments. Do a compression test and adjust the valves if necessary. Finally, check the A/F mixture and if necessary adjust the mixture screw. Make sure you get into "Closed Loop".

[Bitsyncmaster]

A wrong set mixture could do that. Get a dwell meter and check or set your mixture.

[dmcnc]

Also check your timing.

[TheStoot]

A wrong set mixture could do that. Get a dwell meter and check or set your mixture.

I can't check my mixture because the well just shows a set value because i can't get into closed loop

[Michael]

I can't check my mixture because the well just shows a set value because i can't get into closed loop

Well there is a pretty big red flag. Fix that first. Test and diagnose your o2 circuit.

[Bitsyncmaster]

I can't check my mixture because the well just shows a set value because i can't get into closed loop

If it holds (45 deg) with a warmed up engine than probably your O2 sensor is disconnected or bad. Another possible problem (holds 52 deg.) is the wide open throttle switch is always on.