Hello everyone , I bought my 94 Z about a month ago. Recently the car has been missing and jerking pretty bad over 25% throttle. It also surges and shoots to about 1500rpms (even when cold). Temperature seems to fluctuate rapidly but doesn’t overheat. I have replaced fuel filter and plugs. Plugs seemed to be new and looked to be in good shape. No coolant in the oil, no smoke when warm, I’m not thinking head gasket. Earlier today I took my k & n off to clean my throttle body and noticed a lot of moisture underneath/behind the water pump. I’m assuming it’s the opti. Are these normal symptoms of an opti going out? Watched a YouTube video and read some forums but didn’t see anything related to the car surging. I’m going to pay somebody to replace the opti, wires, water pump, thermostat, and thermostat housing. All parts will be reputable as I do NOT want to do this again anytime soon. Any other parts I should replace when the mechanic is down there? Looking for input , I know this is broad and has most likely been covered somewhere. Just looking for some input/advice before I jump the gun thanks.
1994 Camaro Z28
103,000
K & N intake and Borla cat back.

 

At any time have you scanned the PCM for codes?

Is the water pump leaking? Or is this just condensate from high humidity on a cold morning? The water pump leak can enter the Opti, more likely through harness connector tower. In addition to contaminating the Opti, this can help corrode the harness connector. This is more frequent on the 93-94 unvented Opti, where ozone is not being removed by the vent system added in 1995. Have you checked the Opti harness connectors and harness wires for corrosion or damaged pins?

But, both coolant and condensed humidity can simply collect on outdated coil, plug wires, Opti terminals and short circuit the ignition. Could be creating high voltage sparking that can affect the Opti cam position signals.

I've diagnosed three cases of excessive idle surging due to a problem with a batch of MSD Opti caps. Could swing as high as 2,700 RPM at idle. Any high voltage/RFI interference that reaches the Opti cam position sensor can corrupt the signals going to the PCM. This is one case where using an oscilloscope to view the 5 volt square wave signals that the Opti produces can be valuable.

Are you basing the “temperature seems to fluctuate rapidly” on the dash coolant gauge? What are the extremes of temperature, and how fast is “rapidly”? Have you checked the dash gage wire and sensor?

Personally, I'd do a lot more investigation before investing all that money in “parts replacement roulette “. The only reliable Opti available is the one from Petris Enterprises, and somebody recently posted he was out of stock until July 2023. They do offer a package including a water pump.

 

I have not done a scan as the car is not throwing a CEL or SES. Should I get the car scanned anyhow? How can I check the harness around the opti? I’m not very mechanically inclined , hence I’m paying somebody to do the work I believe needs done. The moisture under the water pump seems to be thick , I do not believe it is just water. As for the temperature, I am going off the oem gauge, I do not have a custom temp gauge at the moment. (I do plan to install one). When running for longer than 15 minutes the car will run at the second notch on the oem gauge. (1/4) when idling or sitting at a stop light it quickly raises to (1/2) (190?) it never seems to go above 210 but will raise slightly above the (1/2) line. It is 25 degrees Fahrenheit in Northern Maryland. Thank you for the response.

Another couple symptoms I forgot to mention is I also have no heat! (Assuming a heater core flush will rid that issue)
I smell raw gasoline around the car after it warms up.

 

There are codes, particularly for the Opti and the ICM that do not turn on the SES light.

With regard to the dash temperature gauge, that has its own 1-wire sensor in the driver side head. The PCM uses a 2-wire (more accurate) sensor, mounted in the bottom of the water pump housing. No guarantee the dash gauge is the same as what the PCM sees. The engine is designed to run at 210°F (mid-point of the gauge). Yours seems to be running a bit on the cool side. Are you the original owner of the car? If not someone may have installed a 160°F t'stat, and reprogrammed the fan on/off temperatures in the PCM…. a popular modification, for a few extra HP. Stock t'stat is 180°F, first fan turns on at 226°F and second fan at 235°F. That's for early model year production in 94. Late production runs both fans on low at 226° and both fans on high at 235°.

Your coolant temp sensor for the gauge could be “off”. Easy to check (scroll down below resistance chart):

4th Gen LT1 F-body Tech Articles

Not unusual for heater core to plug up. Can be flushed with a garden hose. Do not get the Opti wet while flushing.

Raw gas smell at the rear of the car can be rotten hoses for the EVAP system charcoal canister in the driver side rear fender. Or someone has deleted the canister, or switched to a vented gas cap. Or, the EVAP purge system is not pulling vented gas fumes through the line to the engine, where it gets dumped into the throttle body.

You can run a pressure test to determine if there are any leaking fuel lines. Just need a fuel pressure test gauge. If the leak is at the fuel pressure regulator, could explain some of your problems.

 

Not necessarily about your present problem, but if you want to keep the car, you will likely need some kind of scan capability. Most mechanics do not have access to those for your car because it is very unique in that regard. I would recommend my app but that requires some talent in using it and some computer ability. Otherwise, a new GM Tech 2 clone from China is a good buy. https://www.aliexpress.us/item/32568...d=64M4DrMZNoeQ

 

Thank you for the help everyone, I will look into a good scanner. I did a heater core flush and it seemed to help a tad, looks like I’ll just replace it as it’s easy to access, thankfully. I just dropped the car off at a reputable mechanic. I’ll update when fixed for other members that may have similar symptoms.

 

So….. rather than follow up with our attempts to help….. you dumped it on a “reputable mechanic”?

Sorry we wasted your time.

 

I’m sorry if you took offense to my decision. Fuel pressure was 44psi at idle (healthy according to other threads) and the car is throwing no codes. I did a heater core flush like you suggested to help with my no heat issue. I’m not very mechanically inclined and I feel like I was a bit over my head. I appreciate your responses, I learned things about my newly acquired car I did not know beforehand. Thank you