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Discussion Starter #1
my 84 AE has had this weird prolbem for about 2 weeks now. the first week it was happening it would die any time it came to idle, i would have to pump the gas to keep it running. i fixed the prolbem of it dieing, there were 2 vacume hoses one was not tight and the other was cracked. so i fixed those. now ONLY SOMETIMES i will start it and it will idle fine and the next min it goes from 700 rpm to 400-500 and the whole car shakes. when i listen to the engine it sounds like that is a vacume leak, but i cant fine anything that looks out of place and my vac/boost gauge says 15-17 (normally at 20) when it is stumbling/hesitating. anyone had this prolbem before or knos what could be wrong and how to fix it?
 

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My friends maxima did something similar when his MAS went haywire..
My 85z acted similar when the fuel temp sensor contact broke.

Take it to a fuel injection specialist, sounds like a bad sensor of some sort is confusing the computer.
 

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"Maybe the same problem this guy is having; Auxiliary air valve by the sounds of it."

All this does is increase the idle speed when cold starting. I've heard it can even be removed and the hole plugged, and the only result will be that it won't idle fast when you first turn it on. As long as the fast idle solenoid is still connected/working, the idle should still jump up when you turn on the lights or a/c. It shouldn't cause any sort of stalling or stumbling.
 

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Discussion Starter #5
i checked the feul temp sensor...with no luck. how do u see if the MAF is acting correctly? how do u check the auniliary air valve?
 

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MAS can be checked with an ohmmeter, and i do not know the correct procedure, but i'm sure google can find it for you.

The Auxiliary Air Valve is in front of the EGR on the passenger side of the intake manifold. It is odd shaped, with a hose on the back and a wire on the front. I seriously doubt this is causing your problem. Its only purpose is to increase idle speed when engine is cold. After the car has been on for 30 seconds, this valve is never used until the car has sat and cooled down again.

I'd bet you have a sensor that is dying. the MAS could definitely be the problem. the CHTS can cause all sorts of weird issues. have you run the diagnostic on the ECU and gotten any feedback? those codes can sometimes save you a lot of time troubleshooting.
 

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Discussion Starter #7
i have read about MAS going out on ppl before and i have heard that the engine does not want to rev past a certin point, is that true? my car drives fine (boosts no prolbem) it is jus when it is idleing that is runs rough.
 

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yeah, if the MAS is dead completely the car will not rev over 2000. But sometimes it doesn't die, it just sends bad information to the ECU, which will cause the ECU to get confused which can cause all sorts of problems. In my buddys maxima, his car would drive fine but would not idle properly and would stall randomly unless he gave it gas at a stoplight. Basically the MAS tells the ECU how much air is entering the engine, and based on how much air the computer knows how much fuel to feed.

Unplug your MAS, if the car will idle ok and rev to 2000, then the MAS is probably the problem.
 

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Discussion Starter #9
from z31.com
On turbos the wire is only cleaned if the car is under 239F, has been above 1500rpm, and has been driven at more than 12mph.

that is exactally when it starts to run fine, after i rev it or drive around. tomorrow i will test it. THANK YOU for the info. i will have results tomorrow.
 

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check timming for the fun of it my 86t would run perfect except at idel it was rough and at cold start i woudl have to hold the gas till it warmed up and it ended up being my timming was off because the stupid timming belt slipped or so i think and well im replacing it tomorrow but resetting the timming really helped
 

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"All this does is increase the idle speed when cold starting."

Yeah that's the function of the part, and a very important one. When the engine warms up this is bypassed as you stated correctly but from what I know it's not "30 seconds" it's whenever the engine is warmed up. If the auxiliary air valve is shot it can cause the car to stall completely, and until fixed you have to compensate with adjusting the idle itself which is obviously not good because when the engines' warm the idle can be too high.

I'm no mechanic but I had this part fail on me not so long ago and the symptoms described above are VERY similar to what I was experiencing until it was fixed.
 

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That horn looking thing in front of the EGR valve is the air regulator and it isn't bypassed when the engine warms up, it actually closes. The Auxilliary air control valve (AAC) is on the other side of the plenum and raises the idle on turbo engines when an extra load is placed on the engine, such as the air conditioner. When the idle goes that low the vacuum falls. That's abnormally normal.

This was just for grins and future reference ;)
I'm pretty sure there's a writeup on Bums site. Might want to check the TPS too.
 

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well that horn looking thing is what i was talking about. It works like a thermostat, and closes when the car is warm. You can remove it and plug the hole, and plug the vacuum line and the car works fine.

that other part, which you are talking about on the other side, IS important and WILL cause problems if its bad.



Post Edited (Oct 10, 5:08pm)
 

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"well that horn looking thing is what i was talking about. It works like a thermostat, and closes when the car is warm. You can remove it and plug the hole, and plug the vacuum line and the car works fine.

that other part, which you are talking about on the other side, IS important and WILL cause problems if its bad"

Well thanks so much for clearing that up for me ;)
 

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Discussion Starter #17
i tested the MAS by starting it (cold) and seeing how it acted, it acted how it normally does at idle boging and hesitating at about 400-500 rpm. i then removed the connector on the MAS and drove it around my block. when i started it it idled at 1000 rpms. when i drove it and got to 2000 rpms it jus stoped and did not want to go past 2000 rpms. i put everything back together, stated it and i started hesitating and idling rough. is the MAS bad or going bad? or is the MAS even the prolbem?
 

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that is exactly what my friends maxima was exhibiting. you disconnect the MAS and it will idle smooth. plug it in and it starts idleing crappy. he replaced it and never had a problem again.
 

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Budget pending I'd personally go for a new one, but thats just me. I dont like using 2nd hand parts period because it could be just as tired as the one your replacing. If you have a limited budget and want to take the risk then go for it. Auction says it's working perfectly so you might get lucky!
 
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