FBody90Formula

i was wanting to see if anyone can help me out..i bought a 1990 firebird formula some months ago.a couple months back it started to idle surge.it will idle at 500 when warmed up and then it will surge from 500 to like 800 back and forth while its idling.when i'm driving everything seems fine runs good no misses.i checked for vaccum leaks everything seems fine there.i put new plugs, new wires, new iat, the cap and button are fairly new also.i would appreciate it if anyone has any suggestions for me..thank you

ShiftyCapone

iTrader: (7)

Well you have covered the basics. When was the last time you checked the timing?

FBody90Formula

as far as i know the timings never been messed with.it didn't start doing this till about a couple months ago.it does it with the stock chip and i also put a tbi stage 1 chip in and it does it with that also..i guess i could check the timing.do you think i could have anything to do with the fuel system?

Z28GEN3

How about the idle air control (IAC)?

ShiftyCapone

iTrader: (7)

Good point. It could be gummed up and or need adjusting. They usually stay put and do not need any adjustment unless they are fiddeled with.

Benm109

It may also be your EGR valve. My car surged at idle on time and I suspected it was the EGR valve so I cleaned it, put it back on, and it has run fine ever since. So, check your IAC and your EGR valve and get back to us.

FBody90Formula

tuesday i put a new IAC and EGR on

FBody90Formula

i've had a couple people tell me it sounds like a vacuum leak.i checked most of the lines they all seemed good.does anyone know of a good way to check for vacuum leaks?

steve8586iroc

You can take a can of wd40 or carb cleaner or almost anything ans spray around all the vacuum lines and manifold base and also at the base of the throttle body.

Steve

novadk13

where the heck is that/hot to check?

xjcamaro89

hey i just fixed this problem in my 89 RS, i changed about every sensor i thought of, but what i did was i busted out the metal cap that hides the idle adjustment screw on the front of the throttle body, its on the front and on the right hand side, its the only metal plug, i just busted it out with a punch, then i turned the torx screw clock wise until it smoothed out, then i played around with that and turning the distributor until i got a good combination of idle, response and power, and now it runs good with a nice idle of 500 RPM, give it a try

FBody90Formula

i'll try what steve said first with the carb cleaner around everything.if i can't get anything there i'll try the idle screw.thanks for everyones comments and help i really appreciate.if anyone else has any other ideas i would love to hear them.i've been struggling with this for a couple months now

Beartracks

I looked at some other posts but my problem might be unique. Getting an intermittant idle surge sometime to as high as 1,800rpm. It seems that the computer is opening the idle air controller. The diverter valve also opens when it happens. I'm thinking it's a water/sensor problem. Happened after a few rainy days. Last time it cleared up after a few dry days. It doen'st miss or stutter, just like you were pushing on the gas.

What the heck could tell the computer to go that fast? I cannot find any dampness on the plug boots, dizzy cap or any sensor connections.

92RS 305TBI

Thanks for any ideas;
Beartracks

Oooops, I meant to start a new post.

FBody90Formula

yes yours sounds worse than mine.mine is just surging from like 500 to 800 and your right it is like your pushing on the gas when it does it

Beartracks

I've been doing a lot or searching and it seems like a rather common complaint although with slightly different symptoms.

Mine started after washing the engine a while back. Wouldn't start till I replaced the ign. module then had the idle problem then cleared up with dry days. It doesn't mke a lot of sense. Since I can find no water and all the sensors have been checked or replaced.

I'm going to take the dizzy cap off again and look for moisture/bad wires. Might have something to do with EGR but seems like that would give a stumbling idle.
I get back to you.

Also I didn't notice it this morning while it was in closed loop. Not till it warmed up. That would indicate a sensor or controll that doesn't work till open loop. Think I'll look at the EGR closely.

FBody90Formula

i just put a new EGR on mine and it's still doing it.but you can try cleaning yours and see if it helps.it started on mine a couple months ago and it seemed like it quit for a couple weeks and then started again

FBody90Formula

well i checked for vaccum leaks and found none.i'm really not sure what to do now

ShiftyCapone

iTrader: (7)

You said you put a new IAC in? Did you just put it in or did you adjust it.

FBody90Formula

i just put it in.it was doing the same thing with the old IAC also..how do u adjust it?

ShiftyCapone

iTrader: (7)

Here you go

Adjusting IAC and TPS

rattle

things that may cause idle surge

1-power steering pressure switch

2-stall saver setting to high

3-a/c request

i would check the power steering switch first, just unplug it
its there to bump up idle when power steering load is high.

FBody90Formula

i'm getting ready to go try the IAC adjustment.i let you know how it goes

FBody90Formula

i did the IAC adjustment.at first i thought it was better.i took it out today and drove it and its still doing the same thing

Wingnutt

Check your TPS voltage setting. If it's a bit high, that will cause the idle to surge. IIRC, the TPS voltage should be set to .54 volts. If I'm wrong, I'm sure somebody will correct me.

FBody90Formula

ok..i'll try that..i guess it can't hurt.when the car is moving is runs great.just at idle it surges and the idle was a little rough feeling today

406-IROC

I had a similar problem with my TPI, and although we're talking about two different set-ups.... the bottom line is that the ECM wants to control everything.

Give you're wiring harness a once over, and make sure you're terminals aren't coming out of their connectors (especially by you're fuel pump relay). If the ECM doesn't get proper feedback, you'll be running in 'limp home mode'.... which results in a terrible surge at idle and low speeds, as well as horrible shifting.

Are you throwing any codes? Is you're SES light on?

FBody90Formula

no i'm not throwing any codes and my ses light is not on.when driving the car it runs good can't tell any problem when driving.it's just at idle the idle is kind of rough and it surges.it staled on me for the first time yesterday taking off from a stop sign.sometimes it boggs down from start and then picks up and is fine

Beartracks

Well mine finally set codes 21 and 42. I checked the TPS voltage and found .4v with throttle closed and 4.5v with it wide open. I started the car and every time the idle jumps up the feedback voltage (blue/black wires) jumps to 3v! I'm assuming nothing other than the TPS could cause this. Maybe a moisture problem. I'll let you know after I change it.

FBody90Formula

i haven't checked my TPS yet..let me know if that solves your problem

Beartracks

Replaced the TPS for $40 and adjusted it and no more problems! I'm going to cut it apart tonight and look for moisture. I found the problem by watching the TPS signal with a digital VOM and observing the voltage jump up the same time the idle changed.

I can post how to check/replace and calibrate if anyone want the info.

ShiftyCapone

iTrader: (7)

Hey good job. If your way of testing it is different than stated in the tech article post it up.

Beartracks

Ooops! This should have been a reply to "idle surge".

Well some might benefit from my tactics. First, as always you need a digital VOM so as not to load up the computer. Get three 3M type "T" wire splices and 3 male spade connector (insulated). Clip the T's on the three wires to the TPS. Put on the spades and slip you VOM probe into the wire end and give it a slight squeeze with pliers. You now have access to the voltage readings. The computer sends 5v to the sensor on the light gray wire, black is ground and blue is the return. With the key on/engine off you sould see 5v between the black and the gray. Between the blue and black the return should be about .5v with throttle closed and a little over 4v wide open. It should change smothly as you open the throttle. If that part is OK start the car and monintor the return voltage. If the idle changes at the same time the voltage jumps you have a problem with the TPS. This problem is probably related to moisture. The other common problem would be wear which would give eratic readings as you change the throttle.


Life is good! See you next time I break something.

Bear Tracks

Beartracks

See "how to" post.

ShiftyCapone

iTrader: (7)

Threads have been merged

FBody90Formula

thanks for that info beartracks i guess thats what i'll do now