Hesitation on part throttlehttp://corvettemechanic.com/forum/images/smilies/banghead.

[ChuckG]

I swapped my stock TB for a 52 MM, changed my injectors to new 24LB Bosch new style, and now I have a hesitation on part throttle and less than solid idle.

My fuel pressure is set at 40lbs, the fuel pump is a new AC Delco. The O2 sensor is new, and the TPS is at .54v. The TPS and the IAC seem to be okay, but they're Standard Products, not AC Delco. Can there be a variance there?

Should I up the pressure? Should I look elsewhere? The car seems to run strong when I get up on the cam at about 2200RPM and times when I depress the throttle harder. Of course, this isn't always practical in traffic.

[c4c5specialist]

HI there,

I would be looking to see what your MAF sensor frequency is running and if its dipping a bit.

Thats where we would recommend starting.

Allthebest, c4c5

[ChuckG]

Thanks Paul--how do I test that? The MAF is rather new and the burn-off relay is functioning well.

[c4c5specialist]

Hi there,

HZ reading on a digital multimeter, starts at idle and as the engine RPM is raised, so does the frequency.

You can use voltage, but its usually not as accurate as frequency.

Allthebest, c4c5

[ChuckG]

Gotcha. Thanks. Will post findings.

Where can I find the numbers I need to see, or is simply seeing the frequency rise with RPM all I need to see?

[ChuckG]

Okay, discovered my MAF has a lifetime warranty, so I simply rep;aced it. Same story.

On part throttle stumble or a little popping, but under a little more pedal pressure, just fine.

Maybe my roller rockers need retightened? Maybe my IAC is bad or not set correctly? Throttle cable gone bad?

[c4c5specialist]

HI there,

Popping ????

Please explain, through the throttle body or through the exhaust ???

Allthebest, c4c5

[ChuckG]

It sounds like through the exhaust. If I gently apply pedal pressure, I get a hesitation something like a stumble, a miss, as if the car is gasping for air or fuel.

If I apply more pedal pressure, the car will surge and run great. I have the fuel pressure set at 40lbs, which I recall is about the same as stock. Maybe the cam and the TB need more? The injectors are new 24lb Bosch--new generation.

If it's relevant, my idle is still all over. Starts at 1200--I can then kick it down, but it hunts between 650-790, usually bouncing in the mid 700s. I expect some with the cam, but not this much.

By the way: I did add a 52MM TB in this. That's about when the problem started. I don;t think it's a defective unit, but probably illustrated a new or missed problem.

[ChuckG]

Okay, upped the fuel pressure from 40psi to 45psi. Rainy, so no test drive yet. I read that 43.5 was factory, so my 40psi was too low even for the 48MM TB, whereas I have a 52MM TB.

Seemed to smooth out some idling, but still hunts a bit.

[ChuckG]

Okay, choking is gone. Now just to tackle the idle.... Think it's mechanical, maybe throttle cable related.