Barely idles when cold

[jim's82]

I'm hoping someone may have a suggestion.... my 82 vette has had about everything imaginable thrown at it to fix it's problem & nothing has worked yet. Every cold start, the engine surges so bad that it sometimes dies without help on the throttle. If I go ahead & throw it in gear & drive before the engine is warm it runs terrible below 1500 rpm & hesitates severely from idle. After the engine warms up it idles much smoother but is still sometimes intermiitant. One minute running smooth & the next picks up a little bit of a rough idle then hesitating from idle (not as severe as when cold). It's a 39K mile car with all original parts except for: new computer, TPS, coolant temp sens., EGR,intake man. gasket, plugs & wires, new dist. cap & coil. What am I missing??? My mechanic says that the fuel injectors are working correctly but he's at a loss now & seems as frustrated with the car as I am. I bought the car last winter for my wife for Christmas.... she hasn't driven it yet!! Any suggestions or insight would be GREATLY appreciated.

PS - My mechanic's last idea was to change the fuel pump although we haven't checked the pressure yet.... I may be looking at this wrong but, I figured since the car runs really bad at idle & runs best at higher rpm's, the demand for fuel at the higher r's wouldn't be met if it can't meet what it needs to idle. Does the fuel pump supply a constant PSI or does it fluctuate to demand? Thanks again, Jim

 

[barrier5]

Had the same problem,finally got mad and wired in an 1989, 7747 ecm out of a pick up.But after all that I thick I can tell you where to look,on the black ecm plug there's 4 wires that control the iac motors ( blue /white stripe,blue/black stripe,green/white strip,green/blackstripe ).Try replacing these terminals,you'll have to take one to a Chev.dealer to match it up.Also theres 2 more I'd do at the same time,one is the brown O2 sensor wire,also on the black plug and the other is the black esc wire on the white plug,it'e the forth wire. I believe what happens is that,being in the battery comp. the wire corrode where they join the term. and give false readings,and i'll bet if you put the car on a scan tool it will read a knock retard. I think that then its get to be like a dog chasing its tail,keeps getting richer to try to get rid of the knock,by retarding the timing and shutting off the air.GM ahd a lot of problems with its nintendo setup thats why it went to the pin type and now the weatherpack term.

 

[jim's82]

I think first I'll try a pressure test on the fuel pump & probably change it. If that's not it, I guess I'll attack the ECM unless anyone can think of something else I should do. One more thing.... if the car is surging at idle, with a pressure guage on, should I see the pressure fluctuating if the pump is the problem or would it just be too low of pressure to feed the need? I may be looking at this wrong but, I figured since the car ran really bad at idle & runs best at higher rpm's, the demand for fuel at the higher r's wouldn't be met if it can't meet what it needs to idle.

PS - I do want to emphasize... the car runs MUCH better once the temp reaches apx. 200 deg. Thanks again, Jim

 

[barrier5]

try looking down the small port on the tb's at idle,see if they look like they're shut.

 

[MoeJr]

You also may try checking the voltage getting to the TPS and see if it erratic. usually surging like that is voltage fluctuation with the TPS. Just my .02

 

[jim's82]

FIXED!!! Just one more question though.

YEA!!!! I looked in to buying a fuel pressure guage & the price was just a little more than a new fuel pump. I decided to just spend the bucks on a new pump without testing the old one. As soon as I started the car after the new pump was installed the car ran better than it ever has, as long as I've owned it!!!!!!! The engine still has a a slightly rough idle but no more surging or hesitating on acceleration. A friend of mine suggested I balance the TB's!?! Does anyone have suggestions for "do it yourself" balancing? My mechanic even admits that he's not real well versed with the requirements for balancing them either. He did say that if I could get some good info on it & it's too much for me to do, he would take it on. So, any & all tips & advise would be much appreciated. Thanks again for the great help & input from everyone helping me troubleshoot the other problems, Jim.

 

[Shadowing1985v]

umm

u mean balance your TPS not your TB right?


i moved my TB its the biggest mistake ever to do,, never touch that, unless someone has before

now i have to put it back to where it was,, sigh

ive had some major problesm with my car,, i replaced everything u could think of,,


but,, if u want to see if your car is fixed or not,, u need to see how fast it can go,,

u should beable to do like around 140 or so with no problem,, or 130,,, ,I replaced my ICM that did alot for me.

 

[Twin_Turbo]

CAn't be the pump. I COULD be a damaged fuel pressure regulator. It's in the rear TB.

I'd check the synchro (balancing) of the TB's 1st. They're pretty easy to balance once you've figured ou how the linkage EXACTLY works. Use a water manometer.

Instructions for setting minimum air: (balancing)
_____________________________________
You'll need a manometer or inches of water gauge, a dremel tool, and a drill.
First drive car until operating temperature is reached.
Ground the diagnostics terminal (closing IAC's) and disconnect both IAC connectors.
You can also use special plugs or a duct tape to plug the IAC (kidney shaped) holes on the TB's. The best would be to do both.
Pop out plug on rear throttle Body by drilling a hole at an angle behind it, then poking something in it to pop it out.
There is another way to remove the plugs without damaging the throttle bodies.
Remove the square vacuum fitting behind the rear Throttle Body for clearane, the front TB's plug can be reached easily.
Use a small drill to makel a hole in the caps and use a small screwdriver and a fulcrum to pop them out.
It maybe a little harder than the other method but it'll keep your Throttle Bodies undamaged.
Break the weld on the balance screw so it can be adjusted.
Put the water manometer on the center port of the rear Throttle Body.
Set the vacuum with idle stop screw to 6 inches of water.
Cap the rear Throttle Body port.
Put the gauge on front Throttle Body center port.
Adjust the BALANCE screw to get 6 inches of water.
Cap all open ports when done.
If you don't have a manometer there is a method to get acceptable minimum air settings. Use this for emergency and have the minimum air set correctly later. Turn both Throttle stop screws until the screw is loose from the linkage. Then turn the balance srew so that both throttle valves are in the same position (fully closed) This position can be found as the position where the linkage connection rod can be moved side to side with the least resistance. Then turn the rear stop screw 1/2 a turn and the front 3/4 of a turn.
Here you can see the rear TB's throttle stop screw:

Here is the original balance screw:

And here's a "new" screw in it's place:

It is NOT recommended to replace the original screw with another one like this. The original screw (when the weld is broken) is much more convenient to adjust that this one. The original screw can be turned by hand easily.
When doing the balancing with a manometer this is how you "read" it:

Figure 2.1 is the situation with no vacuum on the manometer, Fig. 2.2 is not relevant, Fig. 2.3. shows the height h wich must be 6" of water or 0,45" Hg when using a mercury manometer. Here you can see that using the water type manometer will result in a more accurate setting. .

After setting minimum air the Throttle Position Sensor needs to be readjusted. You can read how this is done in the FAQ.
________________________________________________

This comes from my site:
http://www.crossfire.webhop.net or https://www.crossfire.homeip.net if the other link doesn't work
Marck

 

[jim's82]

Thanks Twiinie!!

Thanks for the instructions Twinnie!!! I have a couple of days off from work later next week.... I'll be giving it a try then & I'll definitely let you know how this turns out. You were right, the very next morning, after I thought my car was cured, it ran terrible until the temp hit 200 deg. Could that have anything to do with the "closed loop" VS "open loop"? If so, I can't figure out just what is working & not working in either. One more thing that I haven't mentioned.... I was getting code for TPS & it has been changed 3 times. The first 2 were after market ??brand & I got code from them within a few days. The last is a GM & haven't had a code since. Thanks again, Jim

 

[topless82vette]

what will balancing the tbi's do, Ive never understood this, my crossfire runs very nice so Im assuming it probably just best to leave it the way it is

 

[Twin_Turbo]

Indeed, closed loop is entered when O2 sensor is warmed up & coolant temp is above 175 so 200 could be right.

You can check if the ECM is in open or closed loop. Connect a jumper between the 2 left hand upper ALDL pinouts. If the Check engine light flashes fast it's in open loop (probing O2 for voltage that indicates proper temp. range) when it flashes every second or so it's in closed loop. Don't drive w/ the thing shorted for extended periods though, The engine runs in Field Service mode & the TCC won't work.

A common problem w/ finding the problem is that the code van easily be tripped by something else. However, TPS is usually set when it's too low at idle (0 throttle). It should be 0,525V. Make sure you tighten the torx bolts properly. Also, the TPS has 3 wires, one ground, one 5V and one reference (the one that changes). You can measure the resistance. If you take a look at the values you can determine if there's a "bad spot" in the TPS. It's just a simple potentiometer.

topless,

Balancing assures euqal vac. signal on both TB's and therefore equal fuel distribution. Also, it giveds a more balanced out map signal.

Marck

 

[jim's82]

Twinnie, I'm getting close!!!

While balancing yesterday I got a little confused about the exact order. I have had both TB's set at 6" twice & it ran entirely diferently both times. I first noticed that the rear, when first hooked up, read zero on the guage. I set the rear to 6" then put the guage on the front. I can't remember what it was set at originally but I set that one to 6" using the min. adj. screw in the throt. body. The car ran real smoothe but the idle was at 1000. I then re-read your instructions & saw that there was no mention of adjudting the front.... you said to go to the balancing screw to adjust the front one to 6". I did this & the idle came down (800 rpm) & runs very smooth. But, it went back to hunting idle. The TPS is set at 0.51. Should I have gone back to the rear TB after using the balancing screw & should I ever make any adjustments on the front TB using the min. air adj. screw? I think I'm getting real close to a good running car here. The guy before me had them way out of adjustment obviously. Thanks for your help getting them right.

PS - Do you know if all 82's had an electric fan behind the radiator or was that an option? I'm running at about 212.

 

[Twin_Turbo]

The auxiliary fan is standard on the 82. It's not eCM controleld but switched by a temp switch in the pass. side cylinder head (switched the ground)

I'll explaint the balancing method here. (make sure engine is warmed up before you start)

First make sure you close the IAC's or plug the holes.

You can close the IAC by jumpering the ALDL connetor (jumper test & ground). The IAC's will start to cycle in & out. This is done in a constant motion. Notice the motion and disconnect the IAC connector when the pintle wants to retract, then time it so you reconnect the connector when it's going back (you gotta get the feel for the rhythm )
When done, disconnect the IAC's .

You can also just plug the 2 kidney shaped holes w/ duct tape or so.

Then (you have removed the 2 idle stop screw plugs & the weld on synchro screw) turn the synchro screw one way. Notice wich plate opens (the other will not close because the linkage is stopped by the idle stop screw). Then turn the other way untill the other plate opens. In between these 2 positions is the position where the synchro screw has no effect on the balance. In this position the sideway movement of the rod (perpendicular to the throttleshaft) has the least friction.

Now back off both idle stop screws untill they no longer contact the linkag e(there's a tab on the linkage that will contact the screw) If you've done the above properly both plates will be totally closed. Now using the rear TB stop screw (you can use the fron one too but the entire desciption for front & rear will be turned around!) open the rear plate. The front one will open the same amount. Set it to a very small hairline opening. Start the car, it probably won't idle. Apply the throttle if necessary and feel if it will keep idling. If not turn the idle stop screw some more to open the plates further. If it idles conenct the vac gauge to the rear TB.

Use the manometer to measure the vacuum. Set it to the desired amount (you can set it to less if idle is too high, same value for both TB's is more important than a dead on 6")
Then cap off and put the manometer on the other TB. Now use the SYNCHRO screw to open that plate some more. The other plate won't open (because this plate has the idle stop screw backed off al the way) or close (the stop screw for that plate keeps it from closing) and set it to the desired amount. You can double check some more w/ the manometer.

After done turn the front TB stop screw so it barely contacts at 0 throttle.

You're done

The trick is in the way you turn what and in what order. By using only the stop screw of one TB that one acts as a reference point. It can't close any further. If the stop screw on the other plate wasn't backed off turning the synchro screw so that that plate closes will force the linkage for that plate on the stop screw and the other plate will open. This is what you want to make sure it does NOT happen.

The method is a bit clumsy and tricky because GM use 2 almost identicle TB's and the adjustment can be done from both TB's. This is what commonly makes it confusing.

Marck