I have see a lot of threads for idle issues and have checked everything and pretty much every sensor has been replaced. I have an 87 TPI 5.7 which I can not get to idle good. The RPM are trying to stay around 500 and keeps bumping up to 750 and back to 450 as it almosts stalls. The timing is set correctly and all sensors and even wires have been replaced that may of been bad. Fuel injectors are fine the ohms remain the same when warmed and are all around 16.1 The only ones not changed is maf and knock. As far as i know those should be good. I have been to many shops and no one could figure it out. First found cold start was bad so blocked off and thought promblem was fixed next was vacum leak fixed and then spark plug wires bad still after thinking I had figured out started doing the same thing with idle. Seems to be more so when at operating temp. Any suggestions on what I should look for now?

 

anyone?? I know it's really hard to tell without looking or testing the car yourself but if you have any suggestions it would help.

 

You would probably get some answers if this were posted in the TPI Section. So I will move it for you.

 

thank you! It took awhile to figure out how to post a thread on this site so thanks again for moving it.

 

Is this engine the original? Has it been rebuilt? have you checked your fuel pressure?

 

It has not been rebuilt was a replacement from a transam upgraded the 305 carb I had in it. Eveything has been running fine the last two years I have owned it. Fuel pressure is at 45 is that correct? I have an accel fuel pressure regulator attached to the fuel rail.

 

I have never seen an afpr that has done its job. I would be very suspicious of it. I paid good money to get the factory one but i have no problems with it.

 

anyway of testing the afpr?

 

send some more ideas my way! have the day off to check this out and would like to have running perfect this summer.

 

Do you have the EGR valve hooked up? If so, disconnect it and plug the vac line to the solenoid. Make sure the PCV valve is ok,. You may need to remove the throttle body and clean the back side of it and the IAC seat.

 

Check this website out...Lots of good data...http://users.erols.com/srweiss/tableifc.htm

 

CHECK FOR VACUUM LEAKS AGAIN. AIR IS ENTERING UR ENGINE WITHOUT THE COMPUTER KNOWING. LEANING OUT THE AIR/FUEL MIX.

 

any loss of power along with your idling issues? still pull hard and run strong?

basically what im asking is the idling problem simply an idling problem or are you also losing power or fuel efficiency.

if the latter. it could be possible something like spark plug wires maybe damaged and when heat up maybe missing or arcing on your exhaust manifold, or bad sparkplugs, basic stuff like that, or even something more in depth.

but if the problem is simply an idling problem with no loss of power, then it may very well possibly be a bad idle air control motor.

 

Some good information here but still having problem. All intake parts replaced including all sensors such as IAC and CTS and EGR. Will double check for vaccum leaks but don't think that is an issue. The only thing I could think of is that MAF. spark plugs new along with wires and even distributer is new.

 

I was looking at the wiring for the MAF sensor and had to untape the electrical tape off the wiring to see if the wires are bad. It looks like someone at one time spliced a new harness. Soldiering was bad and noticed some corrosion and a bare wire. Will replace this see if that does anything and let you guys know.

 

Check the IAC wires as well, remove the ECM an check the connections and wires. I think you are on the right path to diagnose the problem. On my 85, I would put my code reader in the ALDL, turn the key on, elect radiator fan comes on, The IAC motor is running,, ,after 60 seconds I unplug the IAC, turn the key off, remove the code reader and crank engine. Mine will idle great with the IAC unplugged like this, but when I shut the engine off and plug the IAC back up and start it,,,The idle starts to vary again. I have the original 19lb injectors in mine and I'm going to switch to Bosch III 22lb and see if it works for me. Another thing to might want to try is check Each injector for seal leakage,, one may be sucking in air.

 

Ok it was the wires to the MAF sensor everything is working great idles around 500 and a little above. Will work on a little more to get the timing a little closer. You can order these from tpiparts.net along with other wire harnesses. I think I am going to replace some other wires too. Thank you for all your help and comments!! Now it is time to burn some rubber!

 

nope that didn't work it was the whole mass flow air sensor and now runs really good. Great deal a CSK or http://www.oreillyauto.com/site/c/de...Stores=true#at only $168 with $55 core. Napa would not even price match so had to wait to have transfered from another store but had the same day. If you need one buy now best deal online!

 

I changed my intake to a 87 version powder coated, put 24lb Bosch III's in from FIC, adj fuel press regulator (36lb@idle), BBK 52mm throttle body with BBK under drive pulleys and Spectre air filters (K&N clones from Autozone $22 ea). All I can say is WOW! what a difference. Smooth as silk and allot stronger.