Hesitation and seeming stutter.

[Paul Higg]

Can anyone help me with this?

If I am at a red light and the limit ahead of me is 55 mph and I PUNCH the gas to get up to 60 as fast as I can, the first one or maybe two seconds I feel a hesitation and what feels like but isn't a backfire. I can punch the gas at 2 mph and it won't happen or punch it at 40 and it won't happen. Just when I am stopped. When I am stopped I am idling at 500 RPM's. I have an LT1 and it is an automatic.

Any help will be most appreciated.

Paul

 

[vetteboy86]

I dont know much about the LT1 but it would seem that it is an off idle condition. Could be related to the throttle position. In other words at idle in gear you are at a certain RPM, at 40 you are at a much different RPM. Even at 2 mph your RPM's are probably a hundred or so higher. Both cases the throttle position is different.

 

[KANE]

Can anyone help me with this?

If I am at a red light and the limit ahead of me is 55 mph and I PUNCH the gas to get up to 60 as fast as I can, the first one or maybe two seconds I feel a hesitation and what feels like but isn't a backfire. I can punch the gas at 2 mph and it won't happen or punch it at 40 and it won't happen. Just when I am stopped. When I am stopped I am idling at 500 RPM's. I have an LT1 and it is an automatic.

Any help will be most appreciated.

Paul

It sounds like your Optispark has moisture in it. I had a 1994 Firebird that did the same thing.

 

[Paul Higg]

Well, that was THE word I didn't want to hear. The dreaded opti. That means a new water pump, opti, and might as well do the wires and plugs while I'm there.

I haven't driven it in the rain. It's been driven in HIGH heat and HIGH humidity. I haven't seen any codes.

Will it only get worse?

 

[Paul Higg]

I dont know much about the LT1 but it would seem that it is an off idle condition. Could be related to the throttle position. In other words at idle in gear you are at a certain RPM, at 40 you are at a much different RPM. Even at 2 mph your RPM's are probably a hundred or so higher. Both cases the throttle position is different.

How would I go about adjusting the throttle position? I'm sure it's in my FSM, just too tired to look it up right now.

 

[Paul Higg]

By the way, that's a BEAUTIFUL car. That C3 style has always been my favorite.

 

[LT4man]

All LT1s have fixed position Throttle Position Sensors. No adjustment possible.

How many miles on your machine? How long have you owned it?

SAVE the gosh darn

 

[Paul Higg]

I bought it in January and it has 91600 on the clock.

 

[LT4man]

Your Optispark distributor is fine!

You have what we call in the auto repair industry: An off-idle bog.

When the throttle plates first tip in, there is a hesitation.

I would remove the Throttle Body from the engine to clean it.

This also makes removing the Idle Air Control Motor a lot easier! You want to clean this while you have it off the engine.

Get your self a can or two of Throttle Body/Carb Cleaner. An old toothbrush or two and go to town!

You will have to drain just a little coolant from your radiator because you have a coolant hose attached to the TB.

Buy a gasket kit from Chris May at Superior Chevy. Comes with all the gaskets you need. (1-800-728-8267) Tell him Gregory from Chicago told you to call him. Or buy them at an auto parts store.

Just make sure the TB is spic & span when you are through!

SAVE THE

 

[Paul Higg]

Thanks LT4man! I will do that as soon as I get a chance as this is the only car we have.

I just sprayed a whole bunch of carb cleaner in there a month or so ago while I cleaned the EGR and the IAC but when I looked in there it was black. I guess I need to do a lot of cleaning!

I appreciate your help.

Paul

 

[LT4man]

Paul, you crack me up!

The black color on the inside is your first clue. The only thing black should be the screws holding the throttle plates onto the shaft.

The throttle body should be aluminum colored & the plates themselves should be gold.

Go git em!

SAVE THE

 

[Paul Higg]

boogie:L

 

[LT4man]

boogie:L

What he said!

You might want to loosen the IAC motor while the TB is still attached to the intake manifold. This will prevent you from putting the TB in a vise and doing terrible things to it!

When you clean the IAC motor, make sure the pintle (pointed finger on the end) faces down while spraying with the cleaner.

Keep track of the round paper gasket or o-ring. A very thin film of oil on the o-ring will help you slide it back into the TB.

SAVE the gosh darn

 

[Paul Higg]

Thanks LT4man! I have printed out your advice.

Paul

 

[Paul Higg]

LT4man, I have a couple of questions. I ordered those gaskets from Chris May as you indicated. I could not get a TPS gasket. Chris told me they are foam. Would it be okay if I cleaned it with it still installed?

The other question. When I was working aircraft we used to clean aluminum with MEK. I don't know how familiar you are with MEK but do you think it would be too strong to clean with? I know there are sensors that are VERY sensitive even to carb cleaner but I can remove them and use it. What is your opinion?

Also, in my FSM it only shows how to remove and replace the throttle body and throttle body extension for a VIN J, I have a VIN P. Is there any difference as far as you can tell?

Thanks.

Paul

Your Optispark distributor is fine!

You have what we call in the auto repair industry: An off-idle bog.

When the throttle plates first tip in, there is a hesitation.

I would remove the Throttle Body from the engine to clean it.

This also makes removing the Idle Air Control Motor a lot easier! You want to clean this while you have it off the engine.

Get your self a can or two of Throttle Body/Carb Cleaner. An old toothbrush or two and go to town!

You will have to drain just a little coolant from your radiator because you have a coolant hose attached to the TB.

Buy a gasket kit from Chris May at Superior Chevy. Comes with all the gaskets you need. (1-800-728-8267) Tell him Gregory from Chicago told you to call him. Or buy them at an auto parts store.

Just make sure the TB is spic & span when you are through!

SAVE THE

 

[LT4man]

Paul, you can remove the TPS and take the foam seal and clean it with your Carb/TB cleaner. It is really only a dust seal. Not a gasket.

I am not familiar with MEK. The TBs are really sometimes only made of very cheap aluminum or pot metal. I would be very cautious. Maybe use it on a nondescript place first.

The letter "J" refers to the LT5 (ZR-1) engine. Same procedure, different TB.

SAVE THE

 

[Paul Higg]

Thanks again LT4man! You've been a great deal of help to me and I appreciate it.

Paul

 

[LT4man]

Thanks again LT4man! You've been a great deal of help to me and I appreciate it.Paul

:cool



SAVE the gosh darn

 

[Paul Higg]

LT4man, I have another question. I looked in the FSM and got an idea about removing the throttle body. Are you talking about removing the throttle body EXTENSION, the piece that's about 8 or 9 inches long with the rectangular cover or are you talking about removing the HUGE aluminum section that the throttle body extension attaches to? If so, after looking at the engine today, it looks like it is not for the faint of heart. I mean, it looks like the fuel rails are on top of it, the injectors are in it, etc.

Paul

 

[Toms007]

If that's what they call it (ie "Extension"), that's what you want to remove. I would call the rest of that the "intake manifold". Removing the TB isn't all that much to do.