Hesitation on take off

[ricksmol]

Hi: I have an '89 SHO to which I have done a lot of work lately. I changed sparkplugs,wires,sparkplug seals and valve cover seals,fuel filter,cleaned the intake manifold, and EGR tube, replaced a flexible EGR connector which was broken, new oxygen sensors and a host of other things.
The car works like a dream in every respect with the exception of one thing...when the car is cold and I step on the gas in first gear the car hesitates and you can hear a very small backfire from the exhaust finally it takes off and from then on it is great.
My question is what can be causing this hesitation? Any ideas?
Thanks
Rick

<small>[ February 24, 2002, 04:13 PM: Message edited by: ricksmol ]</small>

 

[qiksho]

I experience the same thing with my 89 when its cold. It runs pretty rough too. However, I have 120k on mine and have only replaced plugs and wires at around 106k. I figure its because of the oil in my plug wells.

 

[clintonk]

My '90 has developed the identical problem, a hesitation/stumble when I touch the gas pedal from an idle. It only happens when cold, and it otherwise idles and drives fine. On take off, the rpms drop to 400 or so and it has no available power; I have to feather the gas and nurse the rpms to 3k or so before I can move at all. Once warmed up, it drives like new.

In my case, the plugs and wires are new and the wells are dry. With 182k miles and mostly originals sensors (CPS, cam, TPS, O2, MAF, etc) it could be anything, but there are no trouble codes being reported. I'm leaking oil from behind the cam sensor; maybe that's an issue.

Any ideas on how we can track down a problem like this?

Clinton Knight
'90 White 182K
'95 Green 49K

 

[philw349]

I would start with the TPS. That is a very cheap sensor to replace and you can get it tested free at Autozone to see if its even bad. It helped a lot on my low end driveability and shifting. It measures how far the gas pedal is being pressed down basically and sends that to the computer. It takes 5 minutes to get off because its sitting right on the throttle body. You might need vice grips though cause the screws usually strip out.

<small>[ February 22, 2002, 05:50 PM: Message edited by: philw349 ]</small>

 

[SHO SPD]

check to see if the wire is hooked up to the back of the intake on the little black plastic cylinder thing..that was my problem...

 

[MikeTD]

I have this same problem in my 95 mtx. I call it a laggy throttle and it only happens when the engine is cold. Really annoying though. I'd like to get it fixed.

 

[SHO Off]

Well boys, Its nice to know Im not the only one out there with this problem... But Ive Done the whole 60K minus, Waterpump and CPS, and Timing Belt. ALthough Ive got the Stage 2 SHOshop kit, and it only started after the kit was put on... Im thinking its a Fuel related problem... Ie bad 80mm MAF, LPM?... but im going with the TPS next, then trying to swap my 55mm MAF and take out LPM.

 

[noSHO]

I have the same problem, but I'm not sure about the backfire. It has been happening ever since I got the LPM. I give it gas in first and it just doesn't want to go until the secondaries open. Once she's all warm everything is great, all the power is there.

 

[MikeTD]

Well, I just ordered a new TPS and should get it tomorrow (Monday). Hope to put it in when I get it, but I'll have to figure out what to do since I've never replaced the TPS before. Anyone have a brief synopsis for me? Thanks, and I'll let you know if it helps.

 

[ricksmol]

I will try to get a new TPS as well and change it. If that doesn't take care of the problem then I'll have to check further. But it sounds logical to me that the rheostat in the sensor could be worn out after 12 yrs and give the computer the wrong info. It should be easy to change, just unplug the connector and remove two screws.
Rick

<small>[ February 24, 2002, 04:29 PM: Message edited by: ricksmol ]</small>

 

[ricksmol]

Well, I finally found out what the problem was with my car, and it could come handy to others out there.

When I removed the intake manifold, I unplugged all the vacuum lines around it. In the back of the manifold there is a small cylindrical plastic vacuum reservoir ( about 1.5" in diameter) with two lines going to it.

It turns out that I had the lines reversed, the reservoir having a vacuum valve allows flow in only one direction. This prevented vacuum from reaching the correct place and thus the hesitation.

Reversed the lines and my car is running great!

Moral of the story... make sure you plug the vacuum lines in the right place.

Rick

 

[MikeTD]

I replaced my TPS and now everything is great! Took five minutes.