When my car started sputtering and lost power on a part throttle, it would still idle, but very low and roughly. Sounded like it was sputtering and trying to idle higher but instead just dies when the gas pedal was pressed. Happened to be a dreaded SuperRam vacuum leak. When the car was cold, this is when it would have these problems the most.

My guess is that when the car is cold or if it sat off for awhile, the intake gaskets would be thinner, thus leaking out more vacuum. Once fully warmed up and with the coolant/oil temps at 190 degrees and above, the gaskets would have probably expanded and seated well, thus sealing vacuum and with excellent drivability and throttle response.

I was able to simulate this problem by taking off the gasket to the top of the SuperRam plenum and putting it on without bolting it down. Sounded the same way and then the gas was pressed down, it would just die.
Just my $0.05.

 

Well, partly. It's much much better. The rich condition caused by all that unburned fuel/oil mist and fume entering the TPI at idle really loaded it up when hot. After the Seafoam/crankcase cleanout/20-50 oil with restore treatment, the mixture from the PVC valve is much leaner, but not what you get from a new engine. It ran great until the brake booster gave up (2 hours) it leaks vacuum internally I think. I'll know more tomorrow after thats fixed unless they burn up my car completely this time He has a cherry red 94 coupe/auto therefor sale with new paint and tires. If they screw up I'll just take that one

 

I suspected as much. BTW, don't worry that you will insult my intelligence by over explaining things, My lack of knowledge in some areas know no bounds. Even if I know what you are saying, others will benefit. There is that old saw, "Explain it to me like you think I'm stupid"
Please!

 

Great to hear you've solve the problem, for now. I bet being a member in CF has made me a much better problem solver, especially when it has to do with most EFI gasoline powered vehicles.

Example:
Today, I fixed my sister's 2000 VW Jetta 2.0. It stumbled on acceleration and the CEL was on. Also, felt slow and sluggish. It was gonna cost her $1024 and change to fix at the VW dealership, along with all these unnecessary parts and services. They said they couldn't communicate with the ECM and the wiring harness was bad. I took it upon myself to fix the problem by getting the codes read for free at my local Autozone. P1128, MAF sensor malfunction, A/F too lean. I took out the MAF in her car and gave it a little visual. Looked like the MAF had lots of grimy oily sludge on it. Cleaned it up a little and the car still acted the same. I went to the other VW dealer across town and bought a MAF for $83. Installed it. Cleared the codes. Now, no more CEL and better drivability. In fact, it drives like new.

Sorry to hijack your thread, ED...

 

Well it's fixed. I know I've said that before, but this time it is for real. My sputtering when hot was caused by many things that needed fixing anyway since the car has 170,000 miles and most everything was original. Besides the normal major tune up, see original post, the 2 main culprets were:
1. Brake Power Booster and check valve.
2. A problem many of you have on high mileage C4s and don't know it, excessive blow-by. Pull out the PVC valve from the valve cover when it's hot and running and watch the smoke signals appear. Clear air?, you're OK.
This combo caused a rich condition and high idle when stopped in gear. If you have a stick shift it would not be so pronounced.
After yesterdays fiasco with the fire, I was a little worried to return to the same auto repair shop, but they are the only game in town. I needed my brake booster changed, and am not up to it myself as my hands are giving me trouble and I am supposed to be resting them.
They did it in less than an hour, and since the rack was being used, they did it crouching on rough gravel without removing the drivers seat. Ouch, I would have been carried away on a stretcher if I tried that.
I now have BRAKES. I have been driving the car almost a year with a steadly declining brake power booster, and just got used to it I guess. I'm glad it finally failed since the rpm went up 300 when I had my foot on the brake due to a vacuum leak and this contributed to the sputtering. Also I never knew what good brakes this car has. Stops on a dime with very little pedal pressure.
Many of you have chimed in with the same problems and I am happy to report how to fix this.
1. Does you car stop on a dime with light pedal pressure? No? You need (at least) a new power brake booster ($149 at NAPA, one hour shop labor ($90 here). You have an internal vacuum leak and don't know it.
2. I used 5-30 oil since the cap called for it. Older Corvettes in hot climates need 20-50 and an additive (STP, Restore, ect.)
3. The crankcase needs to be flushed out first, follow the directions on the bottle. Install a new filter.
3. The intake and injectors need to be cleaned with Seafoam, available a NAPA stores nationwide. Search Seafoam online for a dealer near you.
It needs to go in the throttle body through either vacuum line, the brake booster line is probably easier. It will smoke like it's on fire. You might want to get this done at a shop to avoid the wrath of your neighbors or a visit from the fire department. This gets all the carbon and gunk out of your TB and injectors.
These changes reduced my blow by from a steady stream of dark smoke (from the valve cover hole) to clear air. This fixed my rich condition almost completely, it's still a high mileage engine. I can live with this. I may get a new engine installed someday if it gets worse, but for now, I'm drivin instead of fixin. I'm taking off the top, let's go for a drive baby!!! WhoHoooo!!

 

Hell Yeah

It's time to