Cruise Control Surging - 1995 Park Ave

[gkook]

The cruise control on my 1995 Park Ave engages but starts surging. The RPMs go way up and down somewhat rapidly, as well as obviously the vehicle begins to pick up speed. It used to work flawless. I have checked all my vacuum hoses, the canister and the one way valve, all is good. I replaced the servo and the problem still continues.

Could this be a bad PCM? I replaced the PCM about three months ago and the first one I got was defective, brought it back to Auto Zone for a new one and the vehicle has been performing perfect since. But I am not sure about their crap products. If it is a bad PCM, could it affect the cruise control without turning on the SEL light? And if there is no light, would it still throw and store codes?

Otherwise, any ideas what else could cause the cruise to surge rapidly?

Thanks.

[maxwedge]

Make sure no slack in any linkage from the cruise to the throttle. Also is the speedo steady when cruising without the cruise on?

[gkook]

Yes, the speedometer is steady when cruising. Also, i just checked and the cables seem to be all tight without any slack.

[Jrs3800]

Has the Throttle Position Sensor been checked out?

[gkook]

I have not checked the TPS because according to All Data diagnostic it is not mentioned. Although, the other day I took out my PCM and brought it back to Auto Zone for replacement, in which the replacement threw on my CEL and made the engine run very rough. But in the two blocks I drove it the cruise did seem to work properly. Since this is the third defective unit in four months from them I returned it for my money back. I have since went to O'Reilly's to order a original AC Delco PCM unit which should be here sometime next week. I will post the prognosis when I receive and install it.

[Bassasasin]

The Cruise computer is in the PCM. The PCM takes in the TPS, VSS signals and uses them. It seems the PCM notes too much acceleration/deceleration it won't set/engage. It makes sense if the VSS is erratic enough to fool the PCM but not the speedometer. Moreover from personal experience, the Multi-Function modules at the base of the turn signal lever fail by wrongfully engaging the accelerate/resume switch.

[gkook]

Thanks for the info about the PCM being the brains for the cruise control. However, I installed an AC Delco PCM; car runs beautiful but the CEL stays on and the cruise still has erratic RPM surging. I then replaced the VSS, but no difference. I am at a loss...do I spend the money for a new TPS or go and spend $70 for an OBD 1.5 diagnostic? Unless does anyone know how to run an on-board diagnostic. I tried the climate control trick, but that doesn't apparently work on a '95 Park Ave.

[Tech II]

What is the code if the light is on?

Not sure on this year.....is the PCM programmable or does it have a PROM?

If programmable, how do you know for sure if it is programmed for your car? You can't be sure, you are hoping they gave you the correct one....

[gkook]

I had a scan this morning and the code was P1640 (quad driver module). I did some research on this and then found that the wire for the EVAP purge selenoid had been chewed through. Either I need to feed the squirrels more or less to keep them from our vehicles? I soldered the wires and viola, the CEL no longer comes on!

However, I am still having the same cruise control issues, sporadic surging of the RPMs. I was hoping to get this figured out before next weekend...long road trip coming up.

FYI...this year had a removable prom, so the PCM is basically plug and play.

[Jrs3800]

If you have the cruise off and are driving at a steady speed ( lets say 70 mph ) does the car surge at all? If not.. Then check the vac lines to the Cruise servo on top of the trans... Make sure they are not deteriorated, follow the line from the cruise module to the port on the rear of the upper intake manifold... If its original its worth replacing..

[gkook]

My car cruises fine at hiway speeds. I already replaced the smaller vacuum lines, but what about the large vacuum line from the servo? Where does that go? Also, in a previous reply it was mentioned about the TPS. Could that be an issue even though the engine runs excellent and there are no codes? I hate to throw money again like I did for the servo and VSS with no change to the irratic cruise surging.

Thanks a bunch.

[Bassasasin]

Originally Posted by gkook

..do I spend the money for a new TPS or go and spend $70 for an OBD 1.5 diagnostic? Unless does anyone know how to run an on-board diagnostic..

I had to get a reader with an adapter for an OBDII and the system was perhaps OBDI signals out. Local parts stores allowed borrowing readers to the parking lot. Someone with wire schematics may be able to figure out that magic wire by comparing that era of vehicle.

Diagnostics are different than some may think.
Check engine simple code readers just read the code. A good shop usually has a deep level diagnostic reader that checks far past the check engine simple code readers and sense quad driver circuit status and report each and give a print out. If this level can be done while driving... you may be closer to your answer.

[Blue Bowtie]

Originally Posted by gkook

...I replaced the PCM about three months ago and the first one I got was defective, brought it back to Auto Zone for a new one and the vehicle has been performing perfect since. But I am not sure about their crap products. If it is a bad PCM, could it affect the cruise control without turning on the SEL light? And if there is no light, would it still throw and store codes?

Otherwise, any ideas what else could cause the cruise to surge rapidly?

I would positively guaranty that AutoZone did not make the "crap" PCM you bought, nor any of the other "crap" you might buy there. There is no AutoZone factory. It's the same "crap" that you can buy anywhere else, including all the other chains, and sometimes even the OEM dealership.

How clean is your TB? How much play is there in the TB shaft bushing?

[gkook]

Update:
Good news…my cruise started working fine at highway speeds after the new PCM. Though originally I had only tested it at 30-35mph on side streets, which it still doesn’t like to stay steady at those low speeds even though all my other GM vehicles have now problem staying on track at 30mph.

Bassasasin:
Thanks for the info, the shop I did bring it to only said it was a ‘quad driver’. But further inspection revealed that the wire for the EVAP purge selenoid had been chewed through by squirrels. Fixing that solved my CEL.

Blue Bowtie:
You are right to a point…Auto Zone does have their ‘Duralast Brand’. Under this manufacturer just off the top of my head I have had to return/replace a battery, wiper, brake rotor, and fuel pump (though after complaining to the district manager they reimbursed me $150 for labor to have the fuel pump re-installed). Although the PCM was a brand remanufactured by Cardone, I do know for a fact that I have had two defective units off the shelf because I was able to swap units and confirm in another running ’95 Park Ave that I used to own and just sold a few weeks ago. The TB could use some cleaning as the throttle sticks ever so slightly when stepping on the pedal slow and light, but the bushings seem tight.

A big thanks to everyone who has replied and for all the suggestions and tips, every little bit helps! Now that my Park Ave just hit 100k and I put new rubber on all corners, it runs and glides like a top.

The only issue left to tackle is the HVAC. Basically after about a half hour on heat, cooler air starts to blow out on the floor and I have to set the temp at 90 degrees to get heat again and then turn back down. Mixing door? I will post this to a new topic, unless someone has a quick suggestion to post.

Thanks again and sorry for the lengthy post!