AC question.

[mhopemk3]

My car idles around 650rpm and when I turn my AC on it drops to 500 or just below. Almost shuts off. When I have to stop as soon as I push in the clutch the car will idle to loww and shut off.

What would cause the car not to Idle up when the AC is turned on?

 

[The Reaper]

i dunno i've always known cars to idle lower with the air on cause its more drag on the engine. my car has never idled below 950 rpm

 

[Nick M]

My car idles around 650rpm and when I turn my AC on it drops to 500 or just below. Almost shuts off. When I have to stop as soon as I push in the clutch the car will idle to loww and shut off.

What would cause the car not to Idle up when the AC is turned on?

The idle up function is not working. It is built into the ECM. The problem is not the ECM though, but likely the signal.

 

[mhopemk3]

Any Idea what connections I would need to check on the ECU?

 

[cjsupra90]

Jet, that is backwards. According to the TSRM, if you get a "51" then you have no "IDL" signal, "NSW" signal or "A/C signal to ECU during diagnostic check.

You can do it like Jet said through the Diag block, but if the car is a manual trans then make sure that the clutch peddle is depressed before you start and during the test otherwise you will get a code 51. The other thing is that if you TPS is out of adjustment to the point that the IDL switch is not functioning, this will also cause you to get a 51.

You can also back probe the ECU and check for voltage when the AC is on. It is the largest of the 3 ECU plugs and it is pin 10, blue with red traces wire. Now this is for the late style ECU with the gray plugs. I am not sure if it is the same for the early style with the yellow plugs.

 

[mhopemk3]

Ok.. any ideas as to what connectors to jumper on the diag block.. Would It be like checking codes? IF so I can do that @lunch.. Just an FYI I do have the grey plug ECU and a brand new engine harness..

Really curious about the TPS possibility. Not sure if that is adj correctly or not. I know a while back I was throwing a 51 due to the tps not being adj properly. I did the whole 2 person watch the codes until 51 is gone yada yada..

Now that i installed the maft pro it seems that the common voltage for TPS is around .45 at Idle and with mine adj it reads .62 @ idle.. May be something to check though.. I know JetJock has had a "few" post on the whole code 51 issue..

 

[mhopemk3]

Yes, jumper the same as checking for codes. You should get a normal code ie; a flash every 1/4 second. Now turn on your AC. When the AC indicator on the climate control panel lights up you should hear the AC clutch click on and the MIL should start flashing code 51. This proves the ECU is seeing the AC "on" signal. It's this signal that is used to idle the engine up.

To check the IDL contact turn off the AC and wait for the normal code to again appear. It takes a few seconds so be patient. When it does press the gas pedal slightly. You should get a code 51. The code should disappear when the pedal is released.

Depressing the clutch as suggested to avoid a code 51 is backwards. Think about it, if you had to depress the clutch to avoid code 51 you would have to do it every time to check for the normal code. Depressing the clutch should give you a code 51, not prevent it. The clutch has two switches on it, one for the starter interlock and the other for cruise control cancellation. Don't hold me to it but as I recall it's the cruise control one that gets tested using code 51.

Fwiw there is no code that I haven't deliberately induced in my car using either my homebrew TCCS simulator, my factory TCCS checker, or the car itself. It's be a while since I've done that though.

I don't follow your statment about TPS "common" voltage. You'll need to explain how you're measuring that.

I got you on the ac testing.. Thanks. The voltage comment is if my tps is adjusted like you say (same as I thought) press the gas a little and get a 51. Then let off the gas and 51 clears the TPS should be right.. If that is true, then my tps shows up at 0.62 @ idle. Now I have been trying to tune my MAFT PRO and most people are saying that the TPS should be @ .40 or .50 which I am not getting. The maft pro shows the TPS info.. My TPS is brand new from Toyota..(FYI).

 

[cjsupra90]

Jet, they might have changed it in the later cars. I did get a 51 every time I did a code scan before I went stand alone unless I did exactly what I said before and the same on my buddies car which was a 91. I can not recall whether or not this was the case on the earlier cars. I dont see why they would have changed it, but I guess that it possible. I have only had a problem on one earlier car that I was working on and had to pull codes and it was several years ago.

 

[cjsupra90]

the TPS "IDL" circuit is really sopost to be adjusted by using a feeler gauge and cheching the continuity between IDL and E2 of the TPS. You should have continuity without the feeler gauge inserted and no continuity with it inserted. I dont remember the exact gauge thickness off hand. I want to say it was like .5mm and below there should be continuity and above 1.0mm the should not be. Somewhere in between is where the change over point should accure.

 

[cjsupra90]

I'm not doubting you cj. If there's one thing I've learned it's that ECU programming was tweak in several ways as the years went by. I can only go by my car, an 87. It's good to know though. Each of us knows something....together we know it all

This is very very ture. And yeah I do agree with one of your earlier posts about missleading info in the TSRM's. I cant recall exactly what but I have come accross a few myself over the years.

 

[mhopemk3]

OK.. I went to the tsrm and I will do the thickness guage adjustment.
.50mm=continuity .90mm=no continuity..

I checked codes and when the ac is turned on it did not throw a code....

Possible issues:
TPS is not adj properly.
Not getting a signal to the ECU

Is this about right?? I will check the ecu connector as well as the tps\throttle adj..

This is :nuts:

 

[mhopemk3]

Well, I'm not surprised it didn't set a code for the AC. After all, it won't idle up and that's where Nick and I said the problem probably lies. The procedure is simply a quick method of checking the wiring before breaking out real test gear.

Are you saying there was no code 51 on the TPS? That's a completely different ECU input so if you didn't get a code 51 with the throttle cracked you have multiple problems. Or it could be the ECU. I doubt it though. Unplugging the TPS with the diag block jumpered should also give you a 51.

Without going into all the details the TSRM procedure for setting the IDL contact is related to emissions. If you don't care about emissions you can set it by using the MIL.

I went ahead and set the TPS that if I press the gas really soft it will throw a 51 and when I let off the gas 51 is gone.. When I turn on the AC no 51.. As you and Nick said.. So I am taking it that there is no signal. What wires should I check? I can check the connections at the ECU but I would rather check other wiring possibilities before tearing the glove box out..

 

[jetjock]

Since you have a TSRM you already have that info. You didn't say what year your car is so all I can go by is my 87 schematics. Look in your book for the real deal.

The AC amplifier sends a signal to the ECU when the AC is on. It's a light blue wire with a red stripe in my car. There is no way to test it without getting up in there. When the AC is on you should have 12 volts between the ECU "AC" input and ground. If not, work backwards until you reach the AC amplifier. If you have voltage there either the ECU is bad or something is wrong with the ISCV. (Keep in mind the IDL contact on the TPS must be closed for the ISC system to work).

If you don't have it at the AC amp the amp itself could be bad. Did you hear the AC clutch come on when you were checking it out? Did the AC light on the climate control panel illuminate? Does the engine idle up slightly or maintain 650 rpm with the headlights or defogger on?

 

[mhopemk3]

Since you have a TSRM you already have that info. You didn't say what year your car is so all I can go by is my 87 schematics. Look in your book for the real deal.

The AC amplifier sends a signal to the ECU when the AC is on. It's a light blue wire with a red stripe in my car. There is no way to test it without getting up in there. When the AC is on you should have 12 volts between the ECU "AC" input and ground. If not, work backwards until you reach the AC amplifier. If you have voltage there either the ECU is bad or something is wrong with the ISCV. (Keep in mind the IDL contact on the TPS must be closed for the ISC system to work).

If you don't have it at the AC amp the amp itself could be bad. Did you hear the AC clutch come on when you were checking it out? Did the AC light on the climate control panel illuminate? Does the engine idle up slightly or maintain 650 rpm with the headlights or defogger on?

I have an 89 and I will start with the ECU voltage check. I did hear the clutch come on and AC light.. I don't see much fluctuation with the defogger or headlights though..

 

[mhopemk3]

Cycle the connectors on the amp and ecu first. Could simply be a tired connection. Then measure them. The defogger and headlight algorithms are designed to maintain idle or just slightly raise idle, unlike the AC which is designed to raise it around 300 rpm. As long as defogger and headlights don't drop the it sounds like they're working. As for the AC, if the clutch worked the odds are the amp is OK so I'm guessing you're looking at a wiring problem. I'm assuming (ya, I know) the idle is high when the enigne is cold and slowly backs down as it warms.

No your right.. It is high around 900 until it warms up.. Where are the amp connectors?

I really appreciate you staying in on this post and helping out... It is like 98degrees here... My damn manifold temps are like a 100..

 

[mhopemk3]

I found the ac amp.. holy crap!! is that behind the dash??

 

[cjsupra90]

on later style ECU's (gray plugs) if every thing is working, A/C on, no code 51. A/C off then you should get a code 51.

If you got no code when the A/C was turned on them you are getting the signal at the ECU.

Try this, being that you adjusted the TPS, then do a scan with A/C off and see if you get the 51.

If the A/C is off, you should get the 51 and with A/C on then no 51.

 

[mhopemk3]

on later style ECU's (gray plugs) if every thing is working, A/C on, no code 51. A/C off then you should get a code 51.

If you got no code when the A/C was turned on them you are getting the signal at the ECU.

Try this, being that you adjusted the TPS, then do a scan with A/C off and see if you get the 51.

If the A/C is off, you should get the 51 and with A/C on then no 51.

Want to make sure I'm clear on this one.. What do you mean "do a scan" are you referring to checking codes?

 

[jetjock]

Yes, that's what he means. Check codes and see if it works as cj says.

Can anyone with an 89+ confirm this? If you jumper the diag block do you get a code 51 with the AC off versus on? Does 51 immediately come up in place of the normal fast blink code unless you hold in the clutch? Can someone try it? I'd like to know because nothing I have in my technical library mentiones this. If it's in fact true it'd be a nice thing to know.

Also, does anyone have Test Mode in their diagnostic block ie; two T terminals for code checking? A T1 and a T2?

 

[mhopemk3]

Check this out.. I went out at lunch and started the code/tps testing and still no 51 with the AC.. BUT!!! what I found was a black wire under the fuse block that was spliced to the big wire coming off the compressor. I traced it back in the cab and found it was tapped into what seems to be the blower fan wiring. So I tuned on the ac with the fan and the clutch clicks and moves slightly (car not running). When I push the ac button on and off nothing changes..

So in short it seems that the previos owner spliced tapped the blower so when you turn on the fan the ac turns on.. Probably why I have a signal problem..

Any ideas where that wire from the ac compressor connects to?? That may be my issue..