Chevy Impala SS Forum banner

1 - 15 of 15 Posts

·
Registered
Joined
·
1,437 Posts
Discussion Starter #1
I was getting a 48 code on my95ss. So I thought I would just clean it the MAF along with the throttle body. BTW I have a Professional Products 52mm that has perforned great. So I took it all apart and cleaned the IAC and took the TPS sensor off and put it right back on. The car ran great for about 5 miles then it was misfiring, bucking and would not hardly run. So I went back through it all---twice. It looked alright. So I went to start it up and now it revs to about 3 grand and dies------I currently have no codes showing. What stupid ignorant thing did I do or what am I overlooking?
 

·
Registered
Joined
·
7,792 Posts
Not stupid, just overlooked. I don't see mention of 'adjust' in your post. Either or both of them will need it after taking them apart.


Check Post#7 here:
https://www.impalassforum.com/vBulletin/2-engine-performance/1240369-idle-issue.html


Read through here for the TPS:
https://www.impalassforum.com/vBulletin/34-engine-problems-maintenance/1270641-tps-sensor-replacement-iac-tb-cleaning.html


And reports are that you can't use just any old carb cleaner around a TB due to bad juju on some of the guts inside. As far as your symptoms it could be as simple as something left disconnected or wiggled loose that you touched while accessing other parts you worked on. After satisfying yourself you've got any adjustments done, one thing I do when a car with a pcm has gone wonky is to disconnect the batt. to "relearn" operations. Not sure of time, but I leave it for maybe couple hours.
 

·
Registered
Joined
·
1,437 Posts
Discussion Starter #3
Thanks for the reply. It was when I was trying to reset the IAC when the car threw its fit and the battery had been disconnected for 4 days. And yes I read both of those links you sent before I even started to clean anything. I used throttle body cleaner. Should I just repalce both the IAC and the TPS?
 

·
Registered
Joined
·
883 Posts
Try the TPS and IAC resets first. On another GM 95 PCM five minutes would reset the PCM. I have not worried about the time on the b bodys. Fifteen minutes should be fine.



And reports are that you can't use just any old carb cleaner around a TB due to bad juju on some of the guts inside.
The MAF is the one that should only see alcohol or a approved MAF cleaner.



I was getting a 48 code on my95ss
This means the engine was running without any signal from the MAF. It would be a long shot if cleaning fixed it. You may have a wiring issue or a bad MAF.


You can run the motor with the MAF unplugged. There are two DTCs for TPS problems.


So you may have a problem with the IAC. First, did you move the pintle in and out when you cleaned it? Movement of this part is NOT recommended by the FSM and many forum members also recommended not moving this part.


So I went to start it up and now it revs to about 3 grand and dies-
This could mean your throttle is not closing or it could be a sign that the IAC has quit working.


Most injected cars will run without either the MAF or the TPS. I expect with both out pretty bad throttle response. But I expect it to idle, maybe higher than normal(1200RPM). Unfortunately if you do not find a problem with the throttle blade being open, you probably have a stuck IAC.
 

·
Registered
Joined
·
1,437 Posts
Discussion Starter #5
No i didn't move the pindle, and it measures 11/8 inch which I understand is what it should be. I have tried the reset on the IAC, but the car wont run enough for that to work. I have it all apart again checking things again as i disassemble. I saw before that the throttle blades were closed so is it possible to install the TPS in a wrong position that it would read that the blades were open causing it to dump more fuel in and thats why on start up it revs right to 3000rpm and then dies for someother reason?

I have check the MAF wiring it is good --so I guess I need a new one of those also.
 

·
Registered
Joined
·
883 Posts
so is it possible to install the TPS in a wrong position that it would read that the blades were open causing it to dump more fuel in and thats why on start up it revs right to 3000rpm and then dies for someother reason?
Signal should be between 0.6V at idle and 5V at WOT. DTC 21 is set if TPS is more than 2.5V at idle. or over 4.8V at key on. So my personal opinion is that the PCM will ignore the TPS if it is out of range. Again you can unplug it for testing. By memory the sensor has a slotted cavity that the throttle shaft fits into. As the sensor can not do a 360deg rotation there should be only one way to put it on.


A stuck IAC will cause the PCM to try to run the engine any way possible and if not shut down.


With the TB blades shut how are you getting enough air to get to 3000RPM? My answer is a stuck IAC is letting the air through.



It was when I was trying to reset the IAC when the car threw its fit
The PCM does not know where the IAC is positioned. The IAC reset causes the IAC to move between full closed and full open. When it hits one end or the other the PCM then just counts a number up or down and expects that the IAC actually moves to where the PCM wants it. So it may now be stuck at a mostly open position.


I an not a mechanic but I have worked on electronic/mechanical systems and my own cars for decades. My experience is with my OEM TB.
 

Attachments

·
Registered
Joined
·
1,437 Posts
Discussion Starter #7
ok I got ya. I will try it with the TPS unpluged and go from there. Trust me you are being a great help!
 

·
Registered
Joined
·
7,792 Posts

·
Registered
Joined
·
883 Posts
Quick look at the TPS. I removed it for the pictures and when I went to replace it I found I had to put it on the shaft then rotate or "clock" it into the position where the screw holes line up with the TPS screw slots. The TPS seems to have a return spring so the TB blades should be closed when installing it. I did not try but I do not think it can be placed wrong.
 

Attachments

·
Registered
Joined
·
1,437 Posts
Discussion Starter #10
Quick look at the TPS. I removed it for the pictures and when I went to replace it I found I had to put it on the shaft then rotate or "clock" it into the position where the screw holes line up with the TPS screw slots. The TPS seems to have a return spring so the TB blades should be closed when installing it. I did not try but I do not think it can be placed wrong.
You are right and that is how I will put in on when I get back to the car
 

·
Registered
Joined
·
6,738 Posts
Don't assume the TPS can't be installed wrong. Are blades closed with throttle untouched? Look,and see to make sure.
 

·
Registered
Joined
·
883 Posts
My personal opinion is do not mess with the IAC unless you are willing to remove it for cleaning. If you just let a cleaner suck in the IAC input and expect it to clean out the passage you might instead cause debris to jam the IAC motor.


I am on several forums and the general view is clean the passage but cleaning the IAC motor could cause damage. I will spray them and very lightly brush them but you do not want to move them or dislodge partials that may later jam them.


When I wanted to do some testing I found IAC motors on flebay for $10. They worked the same as a name brand part. I do not know if they last long. I just put the OEM IAC back in after the test.
 

Attachments

·
Registered
Joined
·
1,437 Posts
Discussion Starter #13
I went ahead and ordered a new IAC I did remove it for cleaning but was very careful not to move the pindle, but maybe I did. Anyway new one in route along with a MAF and a TPS Hopefully that will fix the problem--one that i caused somehow
 

·
Registered
Joined
·
883 Posts
You are right and that is how I will put in on when I get back to the car
In case I am not being clear: when I say unplug something I mean the electrical connector.


The early fuel injected fords surprised me. You could electrically unplug several of the sensors without the check engine light coming on. Unplug the TPS or the MAF and you should get a MIL light. Pull the cable off the battery to clear them later.


For those with a live data scanner you can check the TPS live data, the MAF data, and the IAC numbers. The IAC numbers are just what the PCM asks the IAC motor to move to, not where it actually is. So when the motor does not work properly the IAC numbers will change from stock and may vary from one run to the next.


The IAC parks at a set number(PCM programed) to be ready for the next engine start. The IAC also "follows RPM" to be ready to return to idle when the TB is closed.
 

·
Registered
Joined
·
1,437 Posts
Discussion Starter #15
In case I am not being clear: when I say unplug something I mean the electrical connector.


The early fuel injected fords surprised me. You could electrically unplug several of the sensors without the check engine light coming on. Unplug the TPS or the MAF and you should get a MIL light. Pull the cable off the battery to clear them later.


For those with a live data scanner you can check the TPS live data, the MAF data, and the IAC numbers. The IAC numbers are just what the PCM asks the IAC motor to move to, not where it actually is. So when the motor does not work properly the IAC numbers will change from stock and may vary from one run to the next.


The IAC parks at a set number(PCM programed) to be ready for the next engine start. The IAC also "follows RPM" to be ready to return to idle when the TB is closed.
Oh don't worry you are being clear and helping me more than you know. Thank you for giving up your time and knowledge to help me.
 
1 - 15 of 15 Posts
Top