Hey guys, so lately my car has been idling different each day. Some days on cold starts it will turn on and idle fine, others it will idle at around 1400 drop down to 600-700 shaking and idling likes it's gonna stall and then shoots up to 1400 again repeatedly, it never stalls though. While warming up and the cars cold when I give it gas it has a hesitation in park and in gear. Once it warms up the car is fine and performs great. While on the highway today I noticed it will get up to 55 and when I gave it more gas the motor didn't even react. I hear my fuel pump hum when I give it gas which started happening a week ago but the idle problems have been happening for the whole year I've owned the car. I'm guessing I have low fuel pressure due to a failing pump but I don't think that's what's causing the bad idle that's been happening for a year. I put in a new maf, wires, cap, rotor, fuel filter, transmission, and a few other things I can't think of off the top of my head. The cars a 305 tpi. I plan on testing fuel pressure this weekend on my day off but does anyone have any ideas on what's causing it to idle like that? Iac and tps sensor possibly?

 

You could check both of those (the IAC and the TPS). https://www.thirdgen.org/tpimod2
I would go with the fuel pressure as well and see where that gets you. My car is always a little rough in open loop, which is what your is in when it's surging like that; 'hunting' for the right idle. I know there's a percent change of the AFR vs. temp for open loop and your IAC valve might not be adjusting correctly, or your minimum air speed or TPS might be off. I'd say check those things.

 

My coolant temp sensor is bad, do you think maybe that's causing the problem in open loop?

 

I would say it's possible. If it's sending the incorrect temperature to the ECM compared to what outside temp is, it would enrich/lean the AFR too much, causing the IAC to adjust to find the correct amount of air flow. At least that's my logic behind it. I would replace that, since it's only $11 at AutoZone, especially if you know it's bad. On a side note, I can't ever remember if those fail high or low...

 

Thanks for the help man, I'll rent a fuel pressure tester and buy a temp sensor on my day off

 

It gave me code 44 today, I'm guessing a failing fuel pump not giving me good fuel pressure? Won't be able to test at the rail till saturday

 

Good news, I popped the hood and heard a vacuum leak coming from under the plenum, my guess is it's got something to do with the egr, gonna spray either under it when I get home. I think I found the cause of all this

 

Ha, I was just about to comment that it sounded like a vacuum leak. Glad you got it figured out

 

Yea I'm relieved, just gotta take the plenum off and replace the egr, lines, and sensors under there. I'm gonna have to hold off till I get the gasket kit cause I have a feeling I'm gonna destroy the old ones taking off the plenum

 

Well I got off work and sprayed a whole can of maf cleaner on the vacuum lines and the motor didn't do anything other than surge like it's been doing all along, the leak sounds like it's coming from under the throttlebody

 

ABSOLUTELY this will cause problems in open loop. Back when I first put my headers in the car I accidentally bumped the plug for my CTS and the car would not start without holding the gas down and when you did that it woudl just generally run awful and would only run at like 3000+ RPMs and etc blah blah blah.

Finally found that the CTS plug in the intake had disintegrated and it wasnt getting a good connection. Plugged it back in and it started fine.

 

I don't think it has been cured since I'm having a hard time pin pointing the vacuum leak, I wish it was still only a problem in open loop but just recently the car struggles to increase rpms and gave out code 44 for running lean, I don't have a cat either so it can't be the o2 sensor which seems new. I guess I'll try blowing cigar smoke into a vacuum line and see where that gets me, I'm so close to giving up on this car

 

For what it's worth you can go to autozone and buy a few feet of vacuum line (I personally use 3/8" fuel line because it's stronger) and just replace all your vac lines for less than ten bucks.

 

Ya I was planning on getting vacuum hose, Can I replace the hard vacuum lines with it too? Will 3/8 hose fit on all the connections tightly?

 

Cool. Yes you can, and it should, I'd take a piece of the hard-line in with you if possible just to double check the size. If not you can use 1/4" or put a small hose clamp on the end. I didn't need any clamps or anything though and use it for all my vac lines.

 

If you do buy soft line be sure it's the good stuff, I bought mine at Autozone and it was made by goodyear.

 

Alright thanks for the help man, on my payday I'll pick up a couple feet of 3/8 and 1/4" hose and some connectors as well as a fuel pressure tester. Gonna put a coolant temp sensor in as well just to eliminate that

 

best of luck!

 

I tested my fuel pressure and it's at 47psi with key on motor not running, 41psi idling and when the motor bogs down it jumps up to around 47-50 psi until the idle corrects itself again, when I rev it the motor hesitates and the pressure jumps to 50 and then drops to 41 when the rpms climb, in gear the pressure shakes at 145. once the keys off the pressure stays around 48 and drops very slowly. Anything not normal about that?

 

Stock is 42 psi but 46-50 give better numbers in terms of performance. I think if it's registering 145 then something is off with the gauge, but maybe I'm wrong.

https://www.thirdgen.org/optimal-fuel-pressure

 

Replaced the tps sensor, set it correctly and that didn't change anything, is it true that the idle air control valve lets off a small whistle? Cause I'm hearing something from that general area

 

Check these out, some say don't worry about it, some say it's a vacuum leak:

https://www.thirdgen.org/forums/tech...ling-help.html

https://www.thirdgen.org/forums/tbi/...whistling.html

 

It sounds like a vacuum leak more than a bad bearing but it does sound like it could be coming from the alternator, I'll spray some lube on it and see if it stops for a bit

 

Have you verified the voltage the CTS is putting out?

 

I bought a new cts sensor last week that I'm gona put in on my day off, haven't verified the voltage though, can you run me through the process?

 

I was driving the other night and noticed my headlights flickering, my radio also keeps going into protect mode. while replacing my tranny my alternator randomly started squeeling for a couple start ups and then stopped, could my alternator be failing causing low voltage to the sensors and ignition? i also noticed a ground under my battery, I've been reading that it's supposed to attach to the fender, I must have not noticed it when I put new fenders on, could this have any affect on it as well?

 

So I changed the idle air control valve and the car idled a little bad at startup but it smoothed out and the car ran beautifully in gear and in park, no choppy idle, no hesitation, no code 44, rpms were steady even when I came to a stop sign. Then a couple hours later the car cooled down and I went to go somewhere and code 44 came back along with the surging idle and hesitation. I almost have a feeling that ever since I changed the iac valve if I let it sit and warm up and find it's idle then it won't throw code 44 but if I start it and drive then I get code 44 along with the symptoms, stuck in closed loop? I'm really thinking it's EGR related, can I plug up the vacuum lines going to the egr and drive it to see if it's better?