zekgb

So I've spent the better part of the last month checking off the lingering issues with my car as it has passed the one year mark in my possession. After getting the HVAC vacuum system completely tightened up I figured it was a good time to tackle the Cruise Control which was still inoperative even after the vacuum issues were resolved. So out came the brain for some resoldering. I was a bit uneasy doing the work as it's been a long time since I had a soldering iron in my hand, but it seemed to go well enough and when I put it back in the car for a test drive I could set the speed and it was rock solid, but I couldn't accelerate using the stalk. I decided that that was fine for now as I have a trip coming up next week and have a few other odds and ends to work on.

Now tonight I get in the car for drive and it's not working at all, not even attempting to hold speed. Hmmm that's strange, I guess I'll have to give it another pass with the soldering iron after all. As the sun went down I turned the AC off and a bit later tried the Cruise Control and it set perfectly, not only that, but I could also accelerate from the stalk. I turn the AC back on, the speed stays set but I can no longer accelerate. It's a little late now to start digging into things, but this does seem to be vacuum related correct? Is it possible that the check valve is going bad on the brake booster side and not pulling enough vacuum into the system to completely operate the CC servo and the HVAC recirculation flap circuit? It's definitely not leaking on the other side, nor are there any leaks anywhere else in the system. Anything else I should look at?

AO

Interesting issue. I doubt it's vacuum related, but I suppose it could be.

I took a quick peek at the wiring diagram and don't see how the two are inter-related. Hmmm.... Maybe someone else has better eyes.

rixter

check the vacuum connections in the engine bay just forward of the brake booster, climate control and cruise vacuum lines meet here, you may have one not sitting tight

WallyP

Your first diagnosis is possible - it is not too unusual for the little black/blue vacuum check valve to build up restriction as leaks allow dirt to flow thru. Try cleaning the check valve - it should flow easily one way, not at all the other way.

If that doesn't help, try a leak test on the vacuum line going into the fender to the tempostat (cruise control actuator) and vacuum reservoir. It is not unknown for there to be a slight leak in the reservoir.

It is also very possible that you now have another leak in the HVAC system...

SharkSkin

It's possible that with the AC on, some vacuum circuit is engaged which is effectively a leak -- which you might not notice when doing a static vac test with everything "off". For example, a cracked hose or diaphragm could cause a leak. It might be a leak of just the right size that the AC still works fine by itself but vacuum cannot be maintained against the spring in the servo. It might also be a leak in the servo that cannot be detected until the servo is engaged, again something you would not see in a static "everything off" test.

dr bob

Following Dave's thought process, use your Miti-Vac to pull vacuum on the HVAC system. Activate the AC system with car running, and make sure you can still pump a vacuum. If you can't you very likely have a small tear in one of those fabulous rubber actuator diaphragms.

If the cruise works until you turn on the AC, look at the recirc flap actuator as a most likely candidate for leakage.


You can also follow John Pirtle's tips-page guide for testing the various HCAV vacuum components, and see if any are leaking now that may not have leaked before.

SteveG

Search: There has been much discussion about the vac lines from the check valve thru the firewall to the a/c head controller. One of them is cruise related. Mine would not hold speed. Remove the driver side enter console next to your knee, two screws. When they installed the new radio, shoving it in, pushed the elbow connector off. This was the easist fix I've done in 5 years of ownership.

zekgb

Well that was easy....

I have to admit my initial suspicion was driven by the fact that when I was doing the HVAC vacuum repair that the vacuum coming through the check valve felt weak, but I had no idea how strong it should feel, and once I fixed all the leaky spots, all of the HVAC actuators worked so I figured it was ok. Following Wally's advice I pulled the valve off today and blew into it a few times to see if I could dislodge anything that might have made its way in there and lo and behold it became much less restricted. A test at idle showed a much stronger vacuum being pulled through the check valve than before. On the road the CC now sets and accelerates MUCH harder with the AC on now than it did before with the AC off (I could never get the transmission to kick down before using stalk acceleration, now it does so instantly.)

Pretty much the only time my first thought about where to look for one of these problems has panned out...

SharkSkin

Nice! Now "Drive it like you stole it" and have a beer afterwards.