1994 ragtop/idle erradic and missing at high speed

[anunno]

I just got a 1994 ragtop with 97,000 miles. I am having two problems and I dont know if they are related and I dont know if they are electrical or fuel injected related.

Problem 1: After its warmed up and especially on hot days the idle is erradic when in gear and stopped at lights or in traffic. The engine will race itself from around 700 rpms regular idle to about 2200rpms. The idle will go up and down like it is trying to reset itself or something. I cant tell if the electronic fan is clicking on when this happens but to me the car seems to run a little hot and this happens more often in hot weather.

Problem 2: I just drove from Atlanta to New York and while at highway speeds the tranny is in overdrive. When I punch it for more power to pass or change lanes, the tranny has a hard time downshifting and acutally the engine bucks and chokes... it feel like its missing and stuttering. So I have to ease into picking up speed in the overdrive gear without trying to force the tranny to downshift.

This was happening when I first got the car and since then I had the 100,000 mile tuneup with new platnium plugs, wires and filters and it is still doing the same thing. The GM tech told me I am not running any codes... Any help would be appreciated.

Tony

 

[dilligaf]

My 94 is showing the same symptoms as problem #1. Also when I take off from a stop it occasionally sputters a little, when it starts moving or I accelerate a little harder it smooths out. This just started happening yesterday and like yours, when it seems to get a liitle hot. If I move the shifter into neutral from drive the idle goes back to normal in a few seconds.

 

[Train_Engineer]

I had the same problem with my 94 at about 60,000 miles. After several mechanics stated it could be the opti-spark, I spent the money and had it replaced. I've put on about 6,000 miles since and no evidence of the problem. I would strongly suggest replacing the opti-spark and also your waterpump at the same time.

 

[94Roadster]

I have the exact same problem as #1. Once with the hood up I saw the AC compressor clicking on and off, so I disconnected the AC wire at the compressor. Later it happened again. Today I was in heavy stop and go traffic and it started doing the idle problems so I pulled over and removed the fuse for the Climate control. I got back into traffic and it idles like it's suppose too. This doesn't seem to point to a $900 Opti spark problem, but maybe a loose ground or something else bad in the Climate Control telling the idle to increase because the AC is coming on. I plan on ripping the dash apart this weekend to look for loose grounds/wires since this is intermittent. Any suggestions?

 

[Train_Engineer]

I was also wondering if my problem was caused by the A/C since it mainly occured during hot weather with the A/C on. However, the first instance was during a cool night with no A/C, but with extended slow driving with the engine running on the cooling fans. Typically, my problems occured after prolonged idling (20 minutes or so) or real slow driving for a long time. This allowed the engine temperature to increase above normal (usually around 195 to 200). When in the erratic idle mode, the car would act as if there was a bad plug - it would hesitate on acceleration and would miss at highway speeds under a load. After about twenty minutes of highway driving and getting the engine temperature back down to normal, the missing and hesitation would disappear. I could also just shut the engine off and let it cool down when in the erratic idle mode. When restarted it would work fine, usually for weeks or months until I got stuck in traffic somewhere for a long period of time. My guess is that the opti-spark components where being affected by the engine temperature, and when they cooled somewhat, would work normal. Sine the opti-spark replacement, I have put it through the same conditions as before and have not had any problems.

Tom

 

[94Roadster]

Wow, this sounds exactly like my problem. When I drove in the traffic today it was only 68 degrees so it have much to do with the outside temp. Mine happens just about everytime I drive it. We have considered changing the opti spark, but my mechanic told me that if it didn't fix it that I'd probably hate him for wasting $900. Now I'm not sure what to do. I think I'll still pull the climate control check for wire issues. Did yours also have a starting problem? Last year I'd turn the key and it would fire right up. This year I turn the key and it cranks and sputters and I have to give it about 1/3 throttle for it to start about 95% of the time starting it. I'm thinking its two problems, but maybe not. The fuel pressure and the rest of the fuel stuff has been check more than once without any solution. The O2 sensors were also replaced without any drivablity improvement.

 

[Train_Engineer]

I had no problems starting, hot or cold. I would go for weeks or even months with no symptoms and then 20 minutes at low speeds or idling and it would act up. Put up with it for over a year. I had two separate mechanics look at it and check for codes. It would never place any code, so I had to assume that all of the sensors were working within range. The fuel pump pressure was checked and an injector balance test was done. All were satisfactory. I was aware that these opti-spark units could be a problem. I actually received a letter from Chevrolet around 1996 about a problem with these and that they would replace them within a specific period of time. The time expired before I replaced mine. So I decided in January of this year to replace the opti-spark, along with the water pump, plugs and wires. Runs great and so far with no symptoms of the earlier problems. Of course, each case could be different, so a mechanic should check the engine out completely before decided on the expense of an opti-spark replacement.

Tom

 

[dilligaf]

Well, I talked with my mechanic today and he told me it was the optispark. I am having it replaced along with new plug wires and a new waterpump. After buying new tires yesterday I hope I am through spending money for a while.

Now I am ready to ride.

 

[94Roadster]

Well, it sounds like I need to replace my opti-spark. This car is getting very expensive... This year so far, rear brakes $, all fuilds (brakes, coolant, rear end, transmission, oil) replaced $$, right rear hub $$$, both O2 sensors $$$$, new Eagle F1's all the way around $$$$, now the opti-spark & water pump. And since I'm there plugs and wires $$$$$$$$$$$$$$$$$

I hope I'm done soon with the spending and start enjoying!

 

[dilligaf]

I just left my mechanic, my waterpump was leaking and the optispark bearings were shot. It took a good bit of force to even turn the little disc inside of it. Tomorrow I should be riding again, I hope this one lasts for a while.

 

[Cruise]

Same issue

I also have a '94 auto with 82,000 miles and it is idling erratic, plus it won't downshift from overdrive anymore.
I have replaced the ECM and the TPS and it is still doing it.

Reading the posts above, it is sounding like the opti-spark also.

At the same time the two above issues happened ( after a long road trip ), my ASR stopped working also.

Would the Opti-spark be causing the ASR to mal-function also?

 

[94Roadster]

My mechanic pulled the water pump and found that it has been leaking and that the bearing on the backside was totally shot! The bearing had missing balls and the race was destroyed. I'm glad we replaced it before it had a catastrophic failure. I don't know what the opti-spark looks like yet. But it was running really bad so I'm hoping the opti-spark, plugs and wires cure my problems.

 

[dilligaf]

New opti, water pump, wires, plugs, thermostat, belt, hoses and oil change with Mobil 1, along with a new set of SZ-50 tires. Now it is raining and I can't go out and play. ad

Oh well, maybe it will clear up by the weekend.

 

[94Roadster]

I also had the plugs (gaps about 52 - 64), wires, water pump (bearing shot) and opti-spark (all kinds of rust in there!) replaced it seems to help a lot but I still have starting problems. I turn the key and it cranks over just fine, but I have to give it gas and then it reluntantly starts. I'm not sure what to try next?