My car drives nice on the highway but around town is another thing. It shakes at red lights, so I would say it has a rough idle.
Driving it at low speeds it seams to be searching for what gear to be in so it keeps down shifting & then up shifting.
I assumed the speed sensor needed to be replaced to I picked one up and gave it to my local mechanic to replace since I can not craw under the car and I can't even get it on my ramps. He told me I bought the wrong one, it doesn't fit. I guess there are 2. Maybe one for standard and one for automatic. Mines an automatic. Anyone know a good part number for the speed sensor or do you have any ideas of what else could be causing the transmission to keep shifting at low speeds? I bought mine from Napa. I'm sure I misplaced the receipt.

The mechanic replaced the plugs & wires. I was going to but with my bad back I couldn't do it. ( I broke my back when I was younger) He also put in a new O2 sensor. He said it was bad and his scanner showed that it would not change so he replaced it. I believe him because I did get a code for it before.

Now this is his guess whats wrong with the car. He told me to buy a new optispark distributor and he would put it in.
Does this sound right to you? I wonder if he just wants to do a big expensive job. I hate to say that but if I had a code 16 or if you guys tell me that a bad distributor can cause the car the have a rough idle I would feel better. I am an HEI guy so this distributor truly is new to me.

Having said that I see my year 92 has the expensive non vented optispark. It doesn't look like GM has any in stock so now I am looking at non factory parts and not happy about that. I read both good & bad reviews on AutoZone's Durolast part, same for others. Jegs & Summit both carry their house brand for just under $200. Anyone ever use one of them? MSD is $800 so that's out.

I sure could use some advise here. I'm an old school wrench turner. I never had any issues working on my C3 vette but I am not to proud to ask for help with this.
Thanks guys.

 

There’s a lot of reasons for rough idle and erratic transmission shifting without changing the Optispark - and you’re correct in thinking there’s junk out there. The C4 is nothing like a C3 so it’s best to get that out of your mind set - I went through the same thing until I started reading as much as I could on this site and others. In the case of a C4 you’ll need to pass on as much info as possible: what year, mileage, auto or manual, if you are the original owner- if not how long you have own the car, and in as much detail as possible describe what the car is doing. There’s a lot of C4 owners on here who have gone through the same frustrations you are going through and are more than willing to help you though your problems. Good luck.

 

Thanks BLUDICE,
I have owned this car for a few years. I do not use it regularly, it's not my daily driver but more of a nice Sunday drive for the wife and me. It's a 1992 corvette with the LT1. It's stock as far as the drive train goes. Automatic transmission.

 

A bad optispark will cause misfire and backfires I think your problem is elsewhere

 

[QUOTEA bad optispark will cause misfire and backfires I think your problem is elsewhere][/QUOTE]

I don't think thats the problem either thats why I can here for help.
Don't laugh but I wonder if the injectors may benefit from some cleaner. I'm more of a carburetor guy but have no choice to learn about this stuff now.

 

Yes why not pouring a bottle of fuel injectors cleaner in the gas tank you’ve nothing to lose I like Chevron Techron

 

I just did, I agree nothing to loose and what the heck maybe it can help.

 

I just read someone's post a few days ago about the ASR recalibration solved their rough idle and trans shifting issue. I was hoping it would work on an issue I have on my 92, but turns out the recalibration is an automatic car thing. Mine is a 6 speed. Search for ASR Calibration and you may find the procedure. It is supposed to be in the FSM, but I couldn't find it in mine.

 

 

Thanks FrankieD I will pick up a inch pound torque wrench and try this. I have a couple of big ft lbs wrenches. I have actually built from bare blocks small block Chevy engines back in the day. 35 plus years ago my first build was a small journal crank 67 vette engine 327 030 over. Man that thing would rev!

I truly look forward to trying this and see if it helps. Thanks again

 

Sure looks like the ASR was the issue. Until last week I thought the ASR only effected the traction or wheels sticking to the pavement. I'm old school what the heck do I know if I can't adjust it with a tach dwell meter.

I had some issues adjusting mine but truly believe that was what was causing my car's issues.
The video stated 11 inch pounds. So I had to pick up an inch pound torque wrench. When I set it to 11 inches the car idled as smooth as silk. However it would not shift until high speeds. So I assumed the 11 inch lbs was just a slip of the tongue and he meant 11 foot pounds. Well I had an issue with my torque wrench not clicking and I broke the drill bit and damaged one of the pullies with the 1/8 hole in it..
One interesting thing is only one cable clicked as I set the torque. All 3 had jumped back or loosened when I released them.
I ended up setting the ASR by feel. This reminded me of setting my old 4 barrel carb by ear.
I loosened the torque, the car idles smooth but won't shift.
So I tried to apply more torque until it would shift sooner but not idle rough. This was a few trips around the block but well worth it.
I am happy with my compromise setting.
I would really like to know the correct torque spec so I can tweak this a little better one day.
All I can find for sure is the ASR torque for the LT4 engine. I find a lot of conflicting torque numbers for the LT-1.
I am thinking maybe I need to start a new thread on just the ASR Torque specs for a 92 LT-1.

I want to Thank everyone for taking their time to offer me some much needed help. I appreciate it more than I can express.

 

I just watched again, he stated "71 inch pounds"

 

The problem it seems to be 71 foot pounds not inch pounds., the lt-4 is 35 foot pounds. There is a GM service bulletin that states it for the LT-4.
I couldn't find an official torque spec for the LT-1.

 

I would think anything over 10 ft pounds would damage stuff!, I used my "finely calibrated" elbow and all seems right!