Expert Advice needed
Thread Starter
Instructor
Joined: Jan 2002
Posts: 227
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From: CA
Expert Advice needed
Ok, I posted a little bit ago that the shifting (auto) on my 1990 off the line was kind of delayed. Some people thought it might be a transmission problem but I have more information. Now, as I said above, when coming off the line from a stop the car seems to be about a 1/2 second delayed (usually when the car is up to operation temp.) It also idles alittle ruff. Now, if I put the transmission from OD to 1 and come off the line, it is fine with no delay. Also, when I am at a stop and the car is idling and I put the car in N and rev it up just alittle bit, the engine smooths out and sounds almost perfect and runs very smooth. So I dont know what to think about it. The transmission seems to shift nice an smooth on the highway and in most other situations. Is there a computer problem? Fuel system problem? The problem started after I adjusted the base timing which was off by a bit. I had the timing checked by Chevy in case I set it wrong but they said it was right on the money (much of a shock to me). Any ideas on what it could be or how I can fix it? Thanks!!!
Pro
Joined: Sep 2003
Posts: 670
Likes: 1
From: charlotte nc
Re: Expert Advice needed (C490Vette)
Have you checked the voltage of the throttle position sensor at idle? If it's too low you will get poor throttle response. There is a tech tip as how to set it and also one on increasing the setting slightly for even better throttle response. I would also clean the throttle body if it hasen't been done lately. While you are at it you will need to set the IAC which controls idle speed. This is also in the tech tips. 
Team Owner
Joined: Dec 2000
Posts: 90,675
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From: SE NY
Cruise-In II Veteran
Re: Expert Advice needed (C490Vette)
Your TPS is not adjustable so you cannot use that tweak to enhance throttle response.
Your symptom is a classic of insufficient base timing, even though it's set to factory spec. Bump base timing, with the EST connector open, to around 8 deg BTDC and I bet your throttle response and idle issues are gone.
Your symptom is a classic of insufficient base timing, even though it's set to factory spec. Bump base timing, with the EST connector open, to around 8 deg BTDC and I bet your throttle response and idle issues are gone.
Le Mans Master
Joined: Jul 2002
Posts: 5,818
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From: Alive and well in Burlington NC
Re: Expert Advice needed (65Z01)
Your symptom is a classic of insufficient base timing, even though it's set to factory spec. Bump base timing, with the EST connector open, to around 8 deg BTDC and I bet your throttle response and idle issues are gone.
Also look at the IAC in the throttle body. It might have gotten curded up and the pintel is sticking. Oh what the hell, just pull the whole throttle body and give it a good cleaning. Pretty easy to do.
Thread Starter
Instructor
Joined: Jan 2002
Posts: 227
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From: CA
Re: Expert Advice needed (Steel Blue 91)
Ok, so I thought I would check the car for timing. Just a little test I let the car warm up to op. temp and it began to idle ruff. I shut the car off, unplugged the computer advance for the timing and started the car up again. It was running nice and smooth, so I am assuming that the computer is advancing the timing too much when it gets up to op. temp. So my new questions are...will this incorrect timing cause any permenant damage to my car? Its been like this for about a 3 months or 1500-2000 miles. Would it be ok to drive the car with the computer disconnected temporarily until I can re-time it? (It would only be for 300-400 miles). Would 8 deg. BTC be a good time to set? I dont remember what it was set to before I messed with it, but I am pretty sure the timing is the problem and I need to get it back to where it used to be. Thanks!!!!!!!!! 
[Modified by C490Vette, 12:20 AM 7/3/2004]
[Modified by C490Vette, 12:20 AM 7/3/2004]
Team Owner
Joined: Dec 2000
Posts: 90,675
Likes: 304
From: SE NY
Cruise-In II Veteran
Re: Expert Advice needed (C490Vette)
I only open the EST connector to check/set base timing; I've never driven the car that way (well not intentionally :bb ).
Your engine should idle smoothly with the EST connector open at stock timing of 6deg and more smoothly & a little higher RPM at 8deg BTDC.
However, it should still idle smoothly with the EST connector made too. If not I would suspect a problem in the dist, though with a SD system I'm not sure what effect a faulty MAP would have on idle.
Your engine should idle smoothly with the EST connector open at stock timing of 6deg and more smoothly & a little higher RPM at 8deg BTDC.
However, it should still idle smoothly with the EST connector made too. If not I would suspect a problem in the dist, though with a SD system I'm not sure what effect a faulty MAP would have on idle.
