Ok im not sure whats going on, my car was stalling on a cold start (read other thread) so i bought some throttle body spray cleaner. Ill list exactly what i did if it helps:

undid snorkle from both ends, pulled off throttlebody and PVC vent, i sprayed some cleaner on the plate, back of the plate, IAC port. I let it dry and whiped the grease stuff off with a rag and put the rag on a screwdriver and gently cleaned just the inside of the IAC port (only went in bout 1/2in. I then put the snorkle back on, put the PVC vent back on and connected the other end of the snorkle to the filter. Now, it starts to idle at 2000rpm and drops to 1000-1500... I took it for a quick spin and it seemed to have a little less responsiveness sometimes, i didn't go far at all so cuz i wasn't sure what was wrong so i headed back. The oil temp seemed higher than normal too. What could be wrong? i gotta drive this to work tomorrow. I think i liked the stalling better lol.


and since it'll be asked, the engine is the 2.8L

edit: Kinda on a side note, what is your guys average idle? Was mine lower than normal before so this seems high to me? My idle before was 1000ish, it would drop to 400 and stall. Now it doesn't stall but the idle feels too high to me. About the power loss, that may not be 100% true, i was a little nervous so i didn't really try it out too much.

[This message has been edited by kawana (edited 07-20-2007).]

double post

[This message has been edited by kawana (edited 07-20-2007).]

You are saying its now idling between 1000 and 1500 like going back and forth between the 2? But not stalling?

950-1050 range is good for idle.

[This message has been edited by Hudini (edited 07-20-2007).]

quote Originally posted by Hudini: You are saying its now idling between 1000 and 1500 like going back and forth between the 2? But not stalling?

edit: Ok i payed close attention to it this time and what it seems to be doing is:

start up, 2000rpm>1750>1500 (bout 3-4 seconds)> then it stayed steady at 1100-1200ish, kinda bobbed back and forth.

would it have anything to do with maybe some residue from the cleaner on the inside of the plate that maybe didn't evaporate 100% or something. Its been drying for a few hours now.

If you think this is OK, i might take it for a quick spin and see if the responsiveness feels any better. I was going very easy on it before cuz i didn't know what was going on.

[This message has been edited by kawana (edited 07-20-2007).]

quote Originally posted by kawana: what is your guys average idle? Was mine lower than normal before so this seems high to me? My idle before was 1000ish, it would drop to 400 and stall. Now it doesn't stall but the idle feels too high to me.

Mine idles around 1000 RPM; 400 is too low.

Try this little test. Remove snorkel from the throttle body. Start the engine and let it idle. Place your finger over the IAC port. The engine should quit in short order. This is because you closed off the idle air from the engine. If the engine does not quit then it indicates a vacuum leak somewhere. A vacuum leak will cause a high idle as the IAC is trying to make the car idle down but cannot because extra air is entering somewhere else.

Another thing to try is to remove the IAC from the throttle body. It screws into the throttle body just like a big bolt. It has a gasket on it to provide a seal against air leaking in so be careful you do not tear it. Remove the electrical connector too, it has a little tab you pull back just a bit then pull the whole connector free. Once the IAC is out you can clean the pintle and clean more of the IAC passage. If you need the car tomorrow morning then wait on this step just in case you mess something up you want time to recover.

quote Originally posted by project34: Mine idles around 1000 RPM; 400 is too low.

i know, it was dropping to 400rpm before i used the throttlebody cleaner, i had another thread started cuz it would stall on a cold start. The recommended fix was MAT sensor/throttle body cleaner. I used the cleaner but not the MAT sensor, now that i used the cleaner the RPM is higher as stated in the OP, it doesn't stall now though so thats good. I dont know how i could have messed something up, i didn't touch ANYTHING else besides what i wrote. I was very gentle in what i was doing so as to not damage anything.

Your IAC valve may be headin' south! It was the cause of my high idle problems here. https://www.fiero.nl/forum/Forum2/HTML/084438.html
Hudini...you have a pm
Marc

[This message has been edited by Gokart (edited 07-20-2007).]

The finger test over the IAC port causing the stall is a good thing. It means you have no vacuum leaks.

Ok, if the stalling is cured and the idle is just a tad high then don't sweat it. Drive the car and see if the idle comes down on its own. The ECM is continually trying to adjust idle to perfect. The big test is to see how it acts on a cold start.

quote Originally posted by Hudini: The finger test over the IAC port causing the stall is a good thing. It means you have no vacuum leaks. Ok, if the stalling is cured and the idle is just a tad high then don't sweat it. Drive the car and see if the idle comes down on its own. The ECM is continually trying to adjust idle to perfect. The big test is to see how it acts on a cold start.

Ok.. phew.. big load off my mind lol thanks for your help. This is why i love this forum lol, i never woulda figured this out on my own, especially not in like 20min :P Ill take it for a spin and let you know how it goes.

ok update:

Problem NOT gone, yesterday it was doing fine, idling at around 1000ish. Today, it stalled this morning. It idles at 2000 then drops to 1500 and stays there for awhile. It cant seem to make up its mind, sometimes it idles at 2000, 1500, or 1000. I cant pinpoint the connection for when they idle at those rpms. When i shift into first and give it some gas, it seems to take a bit more that i think it should to get going, it keeps wanting to bog out. going from first into second it kinda "studders" or something, i cant really explain. It doesn't happen all the time, just if im going a little too slow. I thought it was cuz i was going too slow but the RPMs where high enough that it shouldn't have done that.

I hope someone can respond to this soon, i have $300left from my check and am gunna hang onto that cuz i know somethings gunna need to be fixed here. Should i get the MAT sensor, would that be the problem? The Idle doesn't seem to change very much after its been run for awhile, it stays pretty close to 1500, though it does drop down a bit. Someone at work suggested that i get new plugs and wires (but they dont know alot about cars either) but should i do it? Help please! If something needs to be fixed i got all weekend so having it off the road isn't a huge problem. Please speak in lamens terms as much as you can, im still getting used to where/what stuff is. Thanks

Have you got a multimeter? It is an electrical circuit tester. They are pretty cheap from Home Depot, Harbor Freight tools, etc. Especially the analog ones with a dial readout. The digital ones are a little more but easier to read. Plus you can use it again later if you need to test other things.

You can test the MAT sensor with a multimeter. You place the test leads on the little connector pins on the MAT sensor and measure resistance (Ohms). The ECM uses this resistance to read temperature. Look at this scale. Just interpolate between numbers.
The MAT sensor scale is the same as the coolant temp scale so don't let that throw ya.
Its 85 degrees at my house now so that is about 2600 ohms.

[This message has been edited by Hudini (edited 07-21-2007).]

quote Originally posted by Hudini: Have you got a multimeter? It is an electrical circuit tester. They are pretty cheap from Home Depot, Harbor Freight tools, etc. Especially the analog ones with a dial readout. The digital ones are a little more but easier to read. Plus you can use it again later if you need to test other things. You can test the MAT sensor with a multimeter. You place the test leads on the little connector pins on the MAT sensor and measure resistance (Ohms). The ECM uses this resistance to read temperature. Look at this scale. Just interpolate between numbers. The MAT sensor scale is the same as the coolant temp scale so don't let that throw ya. Its 85 degrees at my house now so that is about 2600 ohms.

Ok so i should check the outside temp, then check the sensor and see if it works out to being close to the actual outside temp? Is this correct? Maybe ill go pick one up, wouldn't it be cheaper to just buy the mat sensor lol :P If the sensor is faulty, could this be the cause for the problems ive listed?

The omega is correct, to test the sensor just unplug its connector on the side of the air filter housing and touch your two leads to the contacts on the sensor. Probably easier to get at just by pulling the housing.

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Don't have to take it out. Unplug the sensor,and touch your meter probes to the 2 metel prongs on the sensor.

quote Originally posted by prizm-bluegt: Don't have to take it out. Unplug the sensor,and touch your meter probes to the 2 metel prongs on the sensor.

Ok so i just unplug the back? Like i dont have to unscrew it from the housing? Or am i looking at the wrong thing :P

Using this picture, what part do i need to test?


and, is this the same thing? This is a picture i took:



edit: on my multimeter it says both 2000ohm and 2000k ohm, which do i use? and what do they mean?


edit:2 Im not sure whats going on with this thing, on my drive to the store the idle was fine, hung around 1000 the whole way there and back. The only difference between this drive and the drive earlier in which the idle was 1500 is that it may be slightly warmer outside than it was earlier today. Would the outside temp have this effect on the rpms?

[This message has been edited by kawana (edited 07-21-2007).]

That is the MAT sensor in your picture (sometimes called Air Charge Temp. sensor).
When I was testing it on my car, I found it easier to remove it for testing (spray PB Blaster on threads to help removal)
Once out I use some small electrical clips on the sensor pins and then used some jumpers leads to connected the meter. You will find that the pins are small and close together. I then grabbed a hair dryer to vary the temperature, measuring the change with a thermometer.
I Recorded the the sensor resistance and temperature and found that the readings were close to the posted chart. (sensor working)
One thing with the sensor located under the vent, is can be subject to the elements. Even with the weather seal connector, check for corrosion.

As Hudini has suggested, did you remove and clean the IAC. I found on my car quit a bit of carbon build-up, and cleaned the tip with some throttle body cleaner. (don't soak the IAC in cleaner) Cleaning the IAC, fixing exhaust leaks, and readjusting the stop idle screw cleared up a cold start idle problem. Check that you have a plug for the throttle body stop idle screw.

On your meter, when 2000 is selected, that would be the highest resistance that can be measured on that setting. For measuring at a temp. of 70 deg. F, look for a setting like 10K or 20K.

quote Originally posted by StockGT: That is the MAT sensor in your picture (sometimes called Air Charge Temp. sensor). When I was testing it on my car, I found it easier to remove it for testing (spray PB Blaster on threads to help removal) Once out I use some small electrical clips on the sensor pins and then used some jumpers leads to connected the meter. You will find that the pins are small and close together. I then grabbed a hair dryer to vary the temperature, measuring the change with a thermometer. I Recorded the the sensor resistance and temperature and found that the readings were close to the posted chart. (sensor working) One thing with the sensor located under the vent, is can be subject to the elements. Even with the weather seal connector, check for corrosion. As Hudini has suggested, did you remove and clean the IAC. I found on my car quit a bit of carbon build-up, and cleaned the tip with some throttle body cleaner. (don't soak the IAC in cleaner) Cleaning the IAC, fixing exhaust leaks, and readjusting the stop idle screw cleared up a cold start idle problem. Check that you have a plug for the throttle body stop idle screw. On your meter, when 2000 is selected, that would be the highest resistance that can be measured on that setting. For measuring at a temp. of 70 deg. F, look for a setting like 10K or 20K.

Dunno if you saw but i tried it and got some weird readings. Whats up with that? As far as removing the IAC, how do i do that exactly?

Here's my guess on what's happening with your reading ....

You are using a digital meter with two test probes.
You are hold the test probes on the pins of the sensor for a reading.
As you hold the probes, the connection is not solid, and as you move, ever so slightly the connection changes, and thus the reading.

If you have or can find some tests leads with alligator clips, you would not have to hold the test probes on the sensor.
You may want to clean the pins on the sensor if it has any dirt or corrosion for a better connection.

quote Originally posted by StockGT: Here's my guess on what's happening with your reading .... You are using a digital meter with two test probes. You are hold the test probes on the pins of the sensor for a reading. As you hold the probes, the connection is not solid, and as you move, ever so slightly the connection changes, and thus the reading. If you have or can find some tests leads with alligator clips, you would not have to hold the test probes on the sensor. You may want to clean the pins on the sensor if it has any dirt or corrosion for a better connection.

wow.. your good, thats exactly what was happening lol. I guess ill have to go back and pick some of those up then.

edit: also i was gunna ask. Im not really sure what im supposed to DO with the information i get. How does this tell me if its faulty or not? Im not sure what steps to do here lol. Ill go pick up those clip things now i guess. brb in bout 20min.

[This message has been edited by kawana (edited 07-21-2007).]

quote Originally posted by kawana: wow.. your good, thats exactly what was happening lol. I guess ill have to go back and pick some of those up then. edit: also i was gunna ask. Im not really sure what im supposed to DO with the information i get. How does this tell me if its faulty or not? Im not sure what steps to do here lol. Ill go pick up those clip things now i guess. brb in bout 20min.

If the resistance shown on the multimeter for the sensor is close to the chart readings at the current temperature, then your sensor is good and you will not have wasted money replacing it. If the sensor resistance is way off, then it is bad and needs replacing. Nothing more than that really. The other method is to just start replacing things and hope you have enough money or credit until you find the problem. I never did like that second method as I always bought parts I did not need.

Sometimes you find when taking off a connector that it is the connector itself that has broken or corroded or a bad ground. Lots of good reasons to test before you go buy although it is not always possible.

quote Originally posted by Hudini: If the resistance shown on the multimeter for the sensor is close to the chart readings at the current temperature, then your sensor is good and you will not have wasted money replacing it. If the sensor resistance is way off, then it is bad and needs replacing. Nothing more than that really. The other method is to just start replacing things and hope you have enough money or credit until you find the problem. I never did like that second method as I always bought parts I did not need. Sometimes you find when taking off a connector that it is the connector itself that has broken or corroded or a bad ground. Lots of good reasons to test before you go buy although it is not always possible.

God this car is driving me nuts lol. On the trip to the store it was great, idled perfectly, no lugging between gears like it sometimes does. Aaah. Ok i got the alligator clips, im gunna try this again.

Ok, step one, find the IAC:


Then get a big old adjustable wrench (1 1/4" wrench if you have one)


Unscrew IAC.

quote Originally posted by Hudini: Ok, step one, find the IAC: Then get a big old adjustable wrench (1 1/4" wrench if you have one) Unscrew IAC.

ya i found it, it just wasn't budging and i wanted to be sure that was it before i reefed on it. Didn't wanna unscrew something thats not supposed to come off lol. Ill go do this now.

Well, it did seem better on my drive tonight. The idle was a little lower than before, roughly 950-1100 which was nice to see. Im hopeing this was the problem, there was a good bit of gunk on the IAC so i got it nice and clean. We shall know for sure tomorrow morning.

Ok well i picked up a new MAT sensor yesterday (btw, they said "theres no such thing as a MAT sensor" but i took it out and showed them and they found it, i forget what they said it was called but w/e), it drove home fine with the new sensor. The idle was still around 1500 this morning. Besides that sensor, what is another reason why the idle might be so high on the first start of the day, while later on it will drop to around 1000? I havn't had the sensor in very long so i cant give much more info on how its working, ill know better tomorrow after my run to and from work, we'll see if she's gunna stall again. Is it idling at 1500 bad for the engine? Besides being harder on gas mileage?

It is normal for the idle to be higher on the first start. The ECM adds fuel because a cold engine needs to be richer than a warm engine. How long does it take for it to idle down to 1000 rpm?

The other sensor that plays a role in cold starts is the Coolant Temp Sensor for the ECM. I have read when it fails it faults to the full cold position (-40). If this is true then your car thinks its 40 below and tries to add fuel for that cold of a start. The result is a high idle of course. You can test the CTS the same way as the MAT (those little pins are even the same size, lol) Did I ask you before if you have a laptop? There is free software and a cheap DIY cable you can use to see all your sensor the ECM is looking at.

Can anyone confirm or refute the CTS failing to full cold? Would be nice to know. Here is the CTS:

quote Originally posted by Hudini: It is normal for the idle to be higher on the first start. The ECM adds fuel because a cold engine needs to be richer than a warm engine. How long does it take for it to idle down to 1000 rpm? The other sensor that plays a role in cold starts is the Coolant Temp Sensor for the ECM. I have read when it fails it faults to the full cold position (-40). If this is true then your car thinks its 40 below and tries to add fuel for that cold of a start. The result is a high idle of course. You can test the CTS the same way as the MAT (those little pins are even the same size, lol) Did I ask you before if you have a laptop? There is free software and a cheap DIY cable you can use to see all your sensor the ECM is looking at. Can anyone confirm or refute the CTS failing to full cold? Would be nice to know. Here is the CTS:

Oh ok, ill give it a good run tomorrow. Before i do, i wanna be sure that its not harmful on the engine to let it idle at 1500rpm for awhile to see how long it takes to drop. Also, would it thinking the engine is colder (thus adding more fuel) give off a gas smell at all? I didn't really check, but i think i smelt a little gas today on its first start. Ill give it a good test tomorrow after work, i was a little hesitant at letting it run too long at 1500 before i knew if it was ok or not. What part of the engine am i looking at in that picture? Where is the CTS located exactly? I still got $100 left over from this paycheck so im hopeing getting this fixed wont run over that lol. Guess thats one of the risks at buying a 20yr old car, guess im lucky nothing bigger has gone wrong yet :P The big test will be to see if it stalls tomorrow. Does the depth at which the tip of the MAT sensor goes into the air fiilter houseing have any effect on the temperature it reads, cuz the tip doesn't go in as far on the newer sensor as it did on the old one.

edit: Oh ya, and i do have a laptop, its just sitting in the closet so this could be a good use for it. Please post the details of the software and cable if you could.

[This message has been edited by kawana (edited 07-24-2007).]

All you really need, what you really need, is to look at your ECM. I have a fuzzy feeling that'll help you out IMMENSELY.
Got an ecm, use it man use it gear heads from 30 years ago would kill to have that kind of diagnosis tool!

quote Originally posted by InaneCathode: All you really need, what you really need, is to look at your ECM. I have a fuzzy feeling that'll help you out IMMENSELY. Got an ecm, use it man use it gear heads from 30 years ago would kill to have that kind of diagnosis tool!

please explain HOW i use it lol, i got the laptop, how do i make the plug and what software do i use?

I have no freakin idea All i know is that with the cable and the software, you can look at your ecm. Once you can read the raw data you're golden

Pageing Hudini... got the information about the wire and software? Id like to give this a try. BTW, i think the new sensor did the trick, my idle was still at 1500, but it was moderatly cold out this morning, and after about 5-8min it dropped to 1000. NO STALLING!!! that made me very happy this morning lol, didn't stall or bog down when i gave it some gas. So im hopeing this problem is all done with. Thanks for the help with this issue.