Car loses very noticeable amount of power with a/c on

[billfrank85]

I should also note that on a few occurrences, with the air on...starting the car it immediately dies but restarts with no issues. You have to give it a little gas and then it'll run fine. Never happens when air is off. Seems to coincide with warmer engine and/or ambient air temps. It has been 90-95+ the past several days and I never had an issue when it was cooler. With that I was thinking one of the temp sensors was acting wonky.

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[His Royal Ghostliness]

Only two temp sensors on your engine, passenger-side into the heater pipe fitting is the one for the ECM and the one on the driver side straight into the lower intake is the one for the gauge on the dash. I do not recall if the '91 has a yellow check engine light, if it does and there is indeed an issue with the ECM temp sensors the light should be on. Still it's best to hook a scan tool to it and see what the ECM has to say about all that. But if giving her a bit of throttle fixes the stalling problem I'm thinking there's a good chance the IAC is not playing very nice.

[sly]

+1 if sensors are good, IAC is unhappy or the TB and IAC ports need to be cleaned.

[DerekTheGreat]

The vacuum lines on this car are unfucked with as far as routing goes, and any and all questionable ones have already been replaced. So she should be doing what she's supposed to be doing, but she ain't... Honestly I'm right now questioning how that servo even works, it's got two chambers but only one vacuum line (hooked to one chamber only). And the whole thing can be slid in-out towards the throttle body which in turn turns the same throttle lever the pedal cable hooks up to, that part is easy. Guess I'll be digging into the shop manual to figure out exactly how that stupid thing is supposed to work...

I'll take a dead air raid siren over the loose marbles inside sound this one is making! Does make cold tho, like yours, and there have been other more pressing expenses that already used up this summer's budget (like the damn heat-soaking starter), so not gonna replace it till it actually dies. Which hopefully will be next year at the earliest.

My compressor had the loose marbles thing going on, lasted almost a year and half like that before dying last month. It's even colder now, even in that damn heat wave we had yesterday, was nice.

If you're playing with CFI, definitely make sure the throttle kicker works. You'll have to dig (or ask Pete) but there is a way to jump the appropriate solenoid to ground to verify that it and the dashpot work. There are a couple of adjustments on that thing too. There should be one for the "sled" that the dashpot sits on, and the other one is the plunger tip itself. I want to say the sled is the base idle and the tip is how much it kicks up with AC, but that may be backwards.

Yep, sled is base idle. Did not see a tip on the dashpot when I was messing with mine. I just put a vacuum pump on the dashpot to see it move and then had to manually flip the A/C on to see if the solenoid worked (which it did) on my old '85.

There is vacuum present at the line hooked up to the dashpot, so solenoid obviously works.

What I find interesting is with the engine turned off and no vacuum anywhere, if I disconnect the line from the servo and then step on the throttle the servo's tip will pop out and not retract all the way back in when the pedal is released. This suggest to me the servo may be working backwards, as in the vacuum from the solenoid actually makes it drop back down to low idle, and it's a spring inside that makes it push on the throttle lever when no vacuum is present. But again, shop manual consultation is needed for that. When did all this shit came into existence anyways, '81?

It is supposed to do that, I read somewhere that when you give it throttle vacuum is applied to that dashpot to keep the throttle from just slamming shut should the driver abruptly take their foot off the go pedal. I played around with that with that line plugged and it didn't cause any drivability issues other than it feeling a little jerky like a stick shift car, that's probably why they did it. EDIT: I read that as everything is connected and when you give it gas you see the tip retract out & follow the throttle bracket... Also, are you 100% sure the right lines are going to the right places?

I should also note that on a few occurrences, with the air on...starting the car it immediately dies but restarts with no issues. You have to give it a little gas and then it'll run fine. Never happens when air is off. Seems to coincide with warmer engine and/or ambient air temps. It has been 90-95+ the past several days and I never had an issue when it was cooler. With that I was thinking one of the temp sensors was acting wonky.

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I always shut those things off when cranking. Especially when my car is hot, it will fire up, rev high and then go real low before hitting the idle it wants. All of this happens in like three or five seconds. After that, I flip on the A/C and other electric goodies and go about my business. No problems with that method.

[His Royal Ghostliness]

It is supposed to do that, I read somewhere that when you give it throttle vacuum is applied to that dashpot to keep the throttle from just slamming shut should the driver abruptly take their foot off the go pedal. I played around with that with that line plugged and it didn't cause any drivability issues other than it feeling a little jerky like a stick shift car, that's probably why they did it. EDIT: I read that as everything is connected and when you give it gas you see the tip retract out & follow the throttle bracket... Also, are you 100% sure the right lines are going to the right places?

Can't really see anything the way that stupid air cleaner housing hangs down and covers it all, but what it was doing initially was that the tip as all the way into the servo, and thus throttle closed all the way down bringing idle way too low. This with vacuum applied by the line.

Then I pulled the line off the servo and thus let the servo "normalize" itself any way it wants to, as I stepped on the throttle the servo tip popped out a bit. Upon releasing throttle the tip no longer sinks in as far as it used to, and thus the idle is now very high. It cares not whether vacuum line is connected or not anymore, it just idles at like 1000 RPMs no matter what.

Seeing how the car is now 33 years old, and that I'm reworking the headlights doors control/actuation system due to both the headlights switch and the switchvalve/solenoids assembly leaking vacuum, I wouldn't be one bit surprised if the idle servo is on its last legs. Shop manual will hopefully help diagnose exactly what the issue with it is...

And yeah the vac lines are hooked up correct. They can really only go on in one way, unless someone gets really creative hacking the plastic tubing and extending/shortening it with vac hose, which this one doesn't have that going on.

[gadget73]

I should also note that on a few occurrences, with the air on...starting the car it immediately dies but restarts with no issues. You have to give it a little gas and then it'll run fine. Never happens when air is off. Seems to coincide with warmer engine and/or ambient air temps. It has been 90-95+ the past several days and I never had an issue when it was cooler. With that I was thinking one of the temp sensors was acting wonky.

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Sounds like the IAC is stuck and not bumping the idle up like it should.

[DerekTheGreat]

Can't really see anything the way that stupid air cleaner housing hangs down and covers it all, but what it was doing initially was that the tip as all the way into the servo, and thus throttle closed all the way down bringing idle way too low. This with vacuum applied by the line.

Then I pulled the line off the servo and thus let the servo "normalize" itself any way it wants to, as I stepped on the throttle the servo tip popped out a bit. Upon releasing throttle the tip no longer sinks in as far as it used to, and thus the idle is now very high. It cares not whether vacuum line is connected or not anymore, it just idles at like 1000 RPMs no matter what.

Seeing how the car is now 33 years old, and that I'm reworking the headlights doors control/actuation system due to both the headlights switch and the switchvalve/solenoids assembly leaking vacuum, I wouldn't be one bit surprised if the idle servo is on its last legs. Shop manual will hopefully help diagnose exactly what the issue with it is...

And yeah the vac lines are hooked up correct. They can really only go on in one way, unless someone gets really creative hacking the plastic tubing and extending/shortening it with vac hose, which this one doesn't have that going on.

Hmm, maybe some silicone lube on the retractable tip might help it go back down. Also sounds like someone else was aware of that problem and so they adjusted the idle with it all the way extended, that's how my car was initially. I lubed mine, jogged it several times, let it go back down, disconnected & plugged the vacuum line and then adjusted base idle to roughly what the sticker said it should be. So that part was fine but when I flipped on the A/C it would make the idle too high. Didn't realize the dashpot was adjustable so I lowered the base idle more to compensate for it, certainly not the best thing to do.

My lines were screwed up behind the dashpot closer to the firewall on the drivers side. I had red lines going where the blue lines should be and a section of hose was missing. Wasn't obvious until I looked at the diagram on the hood or core support. Got lucky that there was an unmolested '85 at a yard. '85's are slightly different compared to the earlier stuff.

[billfrank85]

After running Seafoam through the tank and replacing the fuel filter, the problem has gotten significantly better. I still plan on cleaning the IAC valve, replacing the ECTS and oxygen sensors as well.

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[DerekTheGreat]

I bet sly already said this but take the TB off & clean the shizz out of it if you haven't already when you go to clean the IAC.

[sly]

no need to take it off... just engine off... open the throttle and spray a rag with cleaner and wipe out the area behind the valve. Give the IAC ports a couple quick shots off the straw and wipe out the mess. Then crank it up (if not MASS AIR) and with the throttle closed, give the IAC port a few or so half second bursts to get stuff cleaned through it. If mass air... hook up the intake tube and leave the clamp loose... crank it up and let it idle for a bit to clear out any residue... stop... remove the intake tube and hose the IAC ports a little. Repeat a few more times if needed.

[Chuck Norris]

Good throttle body cleaning usually does a motor good. Gotta think of it as a vacuum machine, and with that mindset, having clean, low turbulence passages for air makes a lot of sense. Not having the mechanicals subject to carbon and grime limiting their movement is also vital. Always a winning move.

[billfrank85]

Yeah I'm gonna take everything off, clean, replace gaskets etc.

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