Idle bogs down a lot when A/C is turned on.

[PhoenixRPR]

I have a '92 Eclipse GSX. According to Haynes and Mitsu. spec sheets, the car is suppose to idle up appx. 100 when the a/c is turned on. However, my car bogs down 400 rpms and barely maintains idle. Sometimes, when I hit the a/c button, it bogs so low the car will stall. What factors are involved in the proper functioning of the idle+a/c system?

Note: I have a brand new battery, alternator, ignition coils, idle speed controller (IAC), BISS, EGR valve, ECU caps, and a cleaned out TB. My timing is correct. My base idle is set to appx. 1000 b/c of this a/c problem. If it were set to spec at 750, a/c would be totally inoperable b/c the car would surely stall each time I turn it on.

 

[temfate]

Are you venting the BOV to atmoshere? This is a common first issue...

 

[SpeedFreak03]

Test out your ISC, thats what causes the problem. Is the ISC new or is it from a junkyard/used? http://dmtalon.v8eaters.com/ISC.html

 

[PhoenixRPR]

Definitely not. The car is pretty much bone stock.

 

[PhoenixRPR]

The ISC is brand spankin new from Mitsubishi ($200+) and works properly. A way to verify that it works is that it is suppose to keep the rpms up around a grand while you're coasting to a stop in order to assist your power brakes by having a high enough idle (run-on sorry). The ISC steps at idle properly too. The ISC is not the answer, I wish it was.

 

[PhoenixRPR]

What comes into play when the a/c is on and the car is at idle. What relays, fuses, wires, actuators, motors, could cause such a poor idle with a/c on?

 

[SpeedFreak03]

When you hit the A/C button, the clutch in the A/C compressor engages, which puts a load on the engine. Because of this load, the idle would normally drop, so the ISC returns it back to normal. Maybe something is up with your A/C compressor (could it be putting TOO much of a load on the engine because its seized or something - just a guess)? How old is your A/C belt? I really don't know what the problem could be though, usually a new ISC fixes it. Good luck though!

 

[92awddsm]

Im having the same problem with mine right now and I am in the process of swiching the fiav and isc from a known good car right now. My wife has run to the auto parts store for some hose and tb gasket. I should be done with it in about an hour so I can let you know. The reason Im switching the fiav is because mine is blocked off and Im tired of holding the gas in the morning while it warms up.

 

[SpeedFreak03]

Does your car die if you dont hold the gas down? What does it idle at? Try adjusting your idle: http://www.vfaq.com/mods/BISS-1G.html it should be at 750RPM. I've never heard of having to hold down the gas with the FIAV blocked off, it just takes longer to warm up (from what ive heard/seen/read).

 

[PhoenixRPR]

I read that the fiav cannot be replaced or repaired. Are you replacing the entire TB? my belts are brand new and they aren't off by any teeth. I don't think teh a/c compressor is putting too much load on the engine, but I guess anything is possible. My ISC is working/new like I said so it's not that. When the a/c button is depressed, the clutch engages the compressor, and then a signal needs to pass to the ISC motor to tell it "Wake up and compensate +100 rpms over base idle". The +100 rpms is not fiction, it's in every manual. For some reason the ISC is not receving the message "Get to work idiot". What is along that path?

 

[PhoenixRPR]

92awddsm, please keep us informed with your progress. I want to solve this freaking problem for all dsm'ers.

Speedfreak> I believe that 92awddsm was referring to the Fast Idle Air Valve which is a small wax pellet located at teh bottom of the TB which heats up as the coolant gets hot. This heating causes it to expand and less air will pass through, which in turn will lower the rpms. The fiav is a part that is designed simply to give the car a little extra rpms when the engine is cold by allowing a little bit more air to pass-through the TB. It's similar to how the BISS screw regulates the amount of air that will pass through. But instead of turning the screw, the fiav is self-sustaining and expands/compresses based on temperature. Therefore, holding teh gas down gets the car warmer, faster. Sounds like you are getting the FIAV mixed up with the EGR valve blockoff plate solution some people around DSM country like to do.

 

[92awddsm]

My car idles at 750 rpm all the time, hot or cold. When it is cold, it tries to stall at that rpm. It started as soon as I blocked off my fiav( disconnected water and filled passage) And this I do know from experiance, not what I read, heard, or seen. Im not a newby to this car or working on it, just look at my mod list.

Phoenix, You can replace the fiav. It is the plate screwed to the bottom of the tb with two water hoses going to it.

 

[SpeedFreak03]

92awddsm, sorry I really dont know what is wrong with your car if it idles at 750 like its supposed to. BTW i wasnt puttin u down good luck tho!

Now phoenix, I did a little reading about how the ISC operates. From what I gathered, it sounds like the idle drops, so the ECU opens up the valve (ISC) a little more to let more air in, so the car idles at 750 (or whatever it is set at). Like if its too high, the ECU sends a signal to make the ISC close the valve a bit, and vise-versa. I don't think that the signal is sent because of the A/C, I think its sent because the idle drops, do u know what i mean? So, since all of this is controlled by the ECU, that would lead me to believe bad ECU or leaky caps, but you covered that base too! Do you know where the wire from the ISC goes to? The thing that gets me tho, is that if the idle is fine all the time except when the A/C is on, then the ISC must be working (somewhat) because your idle would be shitty all the time (idle surge), Yea im pretty stumped by this, but if you fix the problem please tell us, im sure you 2 aren't the only people with this issue!

 

[SpeedFreak03]

Speedfreak> I believe that 92awddsm was referring to the Fast Idle Air Valve which is a small wax pellet located at teh bottom of the TB which heats up as the coolant gets hot. This heating causes it to expand and less air will pass through, which in turn will lower the rpms. The fiav is a part that is designed simply to give the car a little extra rpms when the engine is cold by allowing a little bit more air to pass-through the TB. It's similar to how the BISS screw regulates the amount of air that will pass through. But instead of turning the screw, the fiav is self-sustaining and expands/compresses based on temperature. Therefore, holding teh gas down gets the car warmer, faster. Sounds like you are getting the FIAV mixed up with the EGR valve blockoff plate solution some people around DSM country like to do.

Good explaination of the FIAV but I know the difference and it is possible to block off the FIAV, people do it because they say its bad to have the engine idle high when its cold. Here is the FIAV block-off VFAQ: http://www.vallotton.com/fiavblockoff.asp

 

[PhoenixRPR]

Speedfreak> I agree that as the a/c kicks on, the idle would drop, and that is what causes the ECU to tell the ISC to take it up a notch to compensate. That alone made me think it was the ECU. I replaced the caps with a set from machv, but that didn't fix the problem. So I'm wondering about that signal transfer from the ECU to the ISC telling it to change its behavior. So your belief it has nothing to do with any a/c components? It sounds purely electrical to you, like a bad connection from the ECU to the ISC? Which would be weird, as you pointed out, since the ISC seems to do every other task properly. I do not know where the wires go to, I haven't gotten into it that far to trace wires. I don't have typical idle surge. The idle only surges when a/c is on and its fighting to get control over the darn thing.

I've seen that fiav site before. That's actually how I learned about that part. But i guess I have selective memory. The blockoff sounds like a bad idea to me, so I'm glad awddsm is going back to stock. If that fixes the problem, i'd be surprised, since mine is stock and I still have the problem.

 

[DSM_GSX4life]

Your not the only "dsm'er with that problem. But my Idle is all jacked up. After driving it for a while the idle creeps up to 1500 and then goes back down to 1000. and does this over and over. If u figure out the a/c prob let me know" and also if any one has any ideas please let me know! Thanks

 

[PhoenixRPR]

Ok DSM_GSX4Life, I think most of us idle-experienced troubleshooters would agree that your problem sounds like a case of "idle surge". Run a search on teh forums for idle surge and be prepared to do several tests. My .02 is that your Idle Speed Controller is dying.

 

[92awddsm]

Ok, problem fixed for the most part. Idles at about 800 and 775 with ac on. I will readjust the biss tomorrow when I get to work but I just went to get gas, which by the way just went to $2/gal here but I had the ac on and no stalls. That is finally a releif.

 

[DSM_GSX4life]

ONLY 2$ a gallon. U should be happy. Here in SF it is 2.50 and only going up :thumbdown

 

[92awddsm]

yea but last week I payed $1.70/gal for 93 octane at the same gas station. And it is still rising. Im sure it will be $2.5 by memorial day here.

 

[SpeedFreak03]

Yea its rising up here too, it was about $1.65-70 a week ago, now its around $1.80, but wait...thats 87 OCTANE!!! I've heard that its gonna get cheaper in the fall, but who knows. I guess you guys aren't in a rush to fix your A/C then Anyway, thats great you fixed your problem 92awddsm, now we gotta figure out phoenix's problem! And DSM_GSX4life, I'd say its the ISC like phoenix said. Check out this idle surge VFAQ, it has a step by step diagnosis for fixing idle surge: http://www.dsm.org/how-tos/tttt/tttt3.html Good luck!

 

[mitsuclipsegsx]

Is is true you loose HP when u turn ur a/c on?? and if so how much..., 5hp??

 

[92awddsm]

Yes you lose power with ac on unless you are like me and have eprom programmed to cut ac at 90% throttle

 

[SpeedFreak03]

Yep you lose HP, I heard 10%, I'd say about 15HP. But it really kills gas mileage, Ive noticed about 4MPG average on different cars.

 

[PhoenixRPR]

Ok, awddsm, congrats on your apparent fix. Let me know in a week or so of a/c driving if the problem is still gone. If so, do you think all I need to do is replace my FIAV? Do they even sell a FIAV by itself (I don't think they do)? If it was my FIAV, wouldn't I have other symtoms though? Anyone know how to fix this stupid a/c+stall problem. I put a bandaid on my problem by setting base idle to a grand, but that's child's play. I want to get this car running like she should. Any help appreciated.