FAQ: Cruise Control Problems

When you apply the brake it's supposed to release the TCC solenoid. I'm still somewhat leaning towards one of the transmission solenoids, either TCC or Pressure.

If you use the brake and slow down to 50, then manually drop the shifter to 3 do you still have that problem?

I would quadruple check all of your vacuum lines and fittings. Could be problem on the vacuum line to the trans regulator? Other than that I'm pretty much out of ideas.

Please put the year of your car in your signature and whether or not it's supercharged so we don't have to keep scrolling around to figure out which car we are talking about. The '95 SC is different than the rest of ours.

How hard are these to replace? I have a little experience with working on transmissions *WHILE* they are still on the car. I've gone as far as replacing a valve body before, but that's about it.

I just tested it. Braking down to 50 and then putting the gear shifter in 3rd warrants the same powerless scenario. I plan on replacing all the vacuum lines and such. The modulator on the transmission looks like the original one. The rubber hose is a little loose but stays attached. Also, there doesn't appear to be any transmission fluid coming out so the diaphragm is at least somewhat intact. I wanted to replace this as well but don't really want to mess with an adjustable one.

Thanks for all the info so far. It looks like I have a few more things to look into.

Maybe the EGR valve is sticking open. My 95 doesn't seem to store codes for EGR malfunction though it is clearly malfunctioning.

Can the EGR on this car be removed and cleaned like most others?

Yes it can. On the other hand, mine is operating in reverse. The IAC and the EGR should close when accelerating. On my car the IAC and the EGR are opening and are creating a lean misfire.

Nice. Well I'll be cleaning both just in case. Got a new gasket with a screen on the way as well.

If you've replaced a valve body in-car on a FWD setup, you can probably do the solenoids yourself. I would want to be sure it is a transmission problem before replacing any parts though. What if you shift to 2nd instead of 3rd at 50? Do the RPMs increase like they are supposed to but you still have no power?

You could be looking at something else entirely, like a bad fuel pressure regulator. High vacuum causes the fuel pressure to lower, no vacuum causes fuel pressure to increase. When you decel, you have very high vacuum. Maybe something isn't releasing properly.

Now that you can duplicate the problem, you need a scan tool connected to see what isn't happening when it should. That's where it gets tricky, the '95 is OBD-1.5 and very difficult to scan.

I would not open up the transmission unless I knew with absolute certainty that I was going after the right part. Unfortunately for the '95s I'm not sure how to tell you to diagnose further.

What else happens when you step on the brake? Any chance you have a frozen/sticking caliper somewhere? Does the '95 have a brake pedal switch that triggers anything else?

Here's something to test - cruise along at very light throttle at about 60. The transmission should drop into TCC lockup mode. Holding the gas pedal at the same place to maintain cruise speed, tap the brake pedal with your left foot. The TCC lockup should disengage and the RPMs should jump a little bit. If that works, your TCC solenoid is working.

If your other shifts aren't too hard or too soft, the pressure control solenoid is probably okay too. (or does the '95 use the vacuum modulator as a pressure control solenoid??)

edit - the vacuum lines are really critical to your car. Did you check all of the fittings multiple times? You are at the age where the junction tees and fittings made of rubber can all be very brittle and cracking.

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If you've replaced a valve body in-car on a FWD setup, you can probably do the solenoids yourself. I would want to be sure it is a transmission problem before replacing any parts though. What if you shift to 2nd instead of 3rd at 50? Do the RPMs increase like they are supposed to but you still have no power?

The next time I drive, I will downshift to 2nd instead of 3rd and write back with my findings.

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You could be looking at something else entirely, like a bad fuel pressure regulator. High vacuum causes the fuel pressure to lower, no vacuum causes fuel pressure to increase. When you decel, you have very high vacuum. Maybe something isn't releasing properly.

Well, that is sort of why this is so confusing to me. Whenever I enter this "powerless" mode, my engine starts giving off this weird smell...like a rich/exhaust type smell, I really don't know how to explain it...but it is only noticeable during this brief bogged down state.

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Now that you can duplicate the problem, you need a scan tool connected to see what isn't happening when it should. That's where it gets tricky, the '95 is OBD-1.5 and very difficult to scan.

Yes I am very familiar with the annoying OBD 1.5 lol. Getting access to a scanner for when I actually drive will probably be hard. Still looking on a good deal for a compatible one.

I would not open up the transmission unless I knew with absolute certainty that I was going after the right part. Unfortunately for the '95s I'm not sure how to tell you to diagnose further.

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What else happens when you step on the brake? Any chance you have a frozen/sticking caliper somewhere? Does the '95 have a brake pedal switch that triggers anything else?

The smell I mentioned earlier does not smell like binding brakes. I brake at any other speed and have no issues. My rotors all look smooth, no scorch marks or metal on metal anywhere. I am pretty certain it's not brake related but will keep that option in the back of my head when I run out of ideas!

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Here's something to test - cruise along at very light throttle at about 60. The transmission should drop into TCC lockup mode. Holding the gas pedal at the same place to maintain cruise speed, tap the brake pedal with your left foot. The TCC lockup should disengage and the RPMs should jump a little bit. If that works, your TCC solenoid is working.

I have done something similar to this a few times, but I didn't keep my foot on the gas and use my left foot to brake...I will also test it using that method the next time I drive.

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If your other shifts aren't too hard or too soft, the pressure control solenoid is probably okay too. (or does the '95 use the vacuum modulator as a pressure control solenoid??)

Every shift feels great, which is another reason why I am confused. They all feel about the same, just right. No hesitation or slipping or hard and/or weak shifts. From the research I've done, the vacuum modulator is only used during partial throttle shifts or something of that nature. This is another cheap part I am going to replace, definitely before I start tearing into anything else.

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edit - the vacuum lines are really critical to your car. Did you check all of the fittings multiple times? You are at the age where the junction tees and fittings made of rubber can all be very brittle and cracking.

This is also on my shopping list. I replaced one line, the one that goes to the cruise vacuum tank, and one other one because they were split. Replacing all the other ones & the plastic tees is on my to do list as well. Visibly, the remaining ones look decent, but still want to replace for peace of mind. Oh, I also made sure the gasket for the PCV valve cover was good...and it was...also on top of the supercharger is a little black vacuum manifold with a few different vacuum lines going to it. Between this and the SC was a very thin gasket. It broke into several pieces when I took it off, but I made a new one by cutting it out of some Fel-Pro gasket sheets. Are there any pictures or diagrams of all the vacuum lines for a 95? I can pretty much trace everything down to where it goes, but a reference would be great as well.

I planned on doing a lot of this a lot sooner but I injured my knee so it has been a little harder to get around. Now that I am getting better, I will start work on the car again.

Thank you for all of your ideas. It is definitely helping me create a small circle of things to try out, to see what exactly is causing this problem. I love driving the car and I have enjoyed fixing it up so far.

billfrank85 wrote:

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You could be looking at something else entirely, like a bad fuel pressure regulator. High vacuum causes the fuel pressure to lower, no vacuum causes fuel pressure to increase. When you decel, you have very high vacuum. Maybe something isn't releasing properly.

Well, that is sort of why this is so confusing to me. Whenever I enter this "powerless" mode, my engine starts giving off this weird smell...like a rich/exhaust type smell, I really don't know how to explain it...but it is only noticeable during this brief bogged down state.

Hmm. Hmmm. If it really smells very rich during this phase, maybe the fuel pressure regulator IS acting up. Or a vacuum leak. vacuum controls so many things under the hood - fuel pressure, the Boost Bypass valve, transmission pressure... it's really critical.

I'm back to vacuum leaks in my head.

Anyone else more familiar with '95s feel free to add!

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I would want to be sure it is a transmission problem before replacing any parts though. What if you shift to 2nd instead of 3rd at 50? Do the RPMs increase like they are supposed to but you still have no power?

I just tried this. If I shift to 2nd instead of 3rd while it bogs down, my RPM's shoot up (2k+) but I still lack power.

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Here's something to test - cruise along at very light throttle at about 60. The transmission should drop into TCC lockup mode. Holding the gas pedal at the same place to maintain cruise speed, tap the brake pedal with your left foot. The TCC lockup should disengage and the RPMs should jump a little bit. If that works, your TCC solenoid is working.

I tested this as well. If I'm going 60, light throttle, and tap the brake pedal with my left foot...my RPM's jump up momentarily by about 500 or so, then settle back down (lockup re-engaging I'm assuming). So that's good, right?

billfrank85 wrote:

I tested this as well. If I'm going 60, light throttle, and tap the brake pedal with my left foot...my RPM's jump up momentarily by about 500 or so, then settle back down (lockup re-engaging I'm assuming). So that's good, right?

Yes. The TCC solenoid and clutch are working properly. And based on your 2nd gear test, it's not part of your problem. Doesn't sound like you have any transmission problems to worry about. Now you need to get a scan tool on there and maybe a fuel pressure gauge and see what's happening in the engine.

Well, until I get some more testing equipment, what about the TPS or even the coils/ignition module? My coils are mismatched. Actually, I'm not sure if they are even the original ones at all. They don't have the white numbering I have seen on other OEM coils. And I know that a faulty TPS would cause a dead spot in the RPM range...but, I would think it was on acceleration as opposed to deceleration.

If you have mostly normal acceleration the rest of the time, those things wouldn't be a factor after slowing down/stepping on the brake.

deekster_caddy wrote:

If you have mostly normal acceleration the rest of the time, those things wouldn't be a factor after slowing down/stepping on the brake.

Hm, well, at least I can probably count them out then. I'm about to go pick up my new vacuum modulator and will be getting new vacuum fittings and lines as well.

I replaced the vacuum modulator and most of the lines. I was only able to take it up the highway and back. I could easily get to 60 mph, but upon braking (just like before) after slowing down enough I would lose power and it would refuse to accelerate. Hmmmmmm.

I wonder if the EGR or EVAP solenoid are hanging up.

ironclyde wrote:

I wonder if the EGR or EVAP solenoid are hanging up.

I'll be cleaning the EGR valve out once the new gasket gets here to see if that has something to do with it. EVAP solenoid, is that the one near the charcoal canister? I've already replaced the purge valve/solenoid, the one above the rear valve cover.

Try driving it with the EGR unplugged. If the pintle is worn the plunger won't seat all the way. Chances are you'll have to replace it. I believe I meant to say the purge valve, over the rear valve cover, near the brake booster.

ironclyde wrote:

Try driving it with the EGR unplugged. If the pintle is worn the plunger won't seat all the way. Chances are you'll have to replace it. I believe I meant to say the purge valve, over the rear valve cover, near the brake booster.

I will try running without the EGR plugged in to see what happens. The purge valve you speak of is definitely the one I replaced. It was causing my P1640, along with a bad boost control solenoid. Both were replaced with ACDelco parts.

Gotcha. I try to use Delphi or Delco parts when they're available.

hey I just sort of jumped in on this thread but I just had the same problem with my 98 Riviera. I didn't do anything to the transmission however I was going to ask you if you have a check engine light on? From a faulty coil pack. I only say this because in my case this year was a misfire on cylinder number 3 and when I pulled the wires on the coil pack for 3 & 6I found that number 6 terminal was very corroded. It would seem as this is a waste spark system that caused the misfire number 3 because of a poor ground through spark plug #6....Its pretty common issue with this engine and an easy fix. Hope this helps if not its something to remember ...

i have da 95sc if cruise is shutting off could be loss of vaccum. As these cars age the intake manifold and valve cover gaskets go poop and as you loose more vac the mixture gets richer to the point it starts to cook the catolytic converter which could be the weird smell. The car will surge and act like it wants to die at stop lights when this happens. The coil packs loose their insulation its a coil of enameled wire like like in any power or stepup transformer over time the enamel from the heat cycling cracks and arcs inside the coil packs they might test fine as is with the plug wires might ohm out fine but also loose their insulation and arc u can see this happening if u pop the hood and have a look at it running at night look for arcs on all the plug wires. I cant stress enough about the vac if she aint sealed up tight she wont run to the tip top and u will just be throwing parts at it.

I would also like to say its not hard to tear down the top end of this motor I did mine over the course of a week all new intake and valve cover gaskets, new vac lines every where just run of the mill crapola from the auto parts store.
New plugs and wires, I also replaced the coupler in the sc u wanna use the black rtv on the sc when replaceing the coupler apply a nice flat coating on the snout surface and let it set up over night then retorque afew times to allow for compression of the rtv it will seal just fine it just takes time and common sense to get these cars up to snuff trust me its well worth it every one where I work has tried to race me down the hiway and not one has been able to out run me rivi from 55 to 100 pulls real hard and when I say hard theres alot of guys where i work who have 2000 model camaros that cant pull my car on the hiway.

THE BOOST!

All the terminals look fine. However, the coil packs are not the OEM ones. They are a mix of aftermarket ones (looks like 2 different brands but same part number interchange). I'll be replacing all 3 plus the module underneath in the near future though. I'm going to clean out the EGR today and see where I'm at.