Can someone help me with the idle speed control of my 350 TPI. Please see modification list below.
I have removed the IAC, cleaned and lubricated the pintle end and shaft. I also sprayed cleaner into the IAC opening and cleaned the passages.
I set the minimum idle air and TPS voltage following the instuctions in the tech article section.
In order to get the minimum idle speed (450-500 rpms) I had to open the throttle level screw several turns.
The problem I'm having is the idle rpm is too high when coming to a stop after driving at freeway speeds. The engine will pull against the brake for a few seconds and then slow down. Sometimes when it does slow down it will idle too low and the engine runs a little rough when this happens. One time the computer set a code 23 when this slow idle condition occurred. One other time the check engine light came on and stayed light until I turned the engine off and restarted it.
Any suggestions???

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87 GTA, 350 TPI, auto, 3:27 gears, rebuilt engine, ZZ3 cam, LT4 valve springs, pocket ported stock heads, edelbrock intake, TPIS air foil, AFPR, high flow air cleaner, modified stock air canister, relocated air intake sensor, tb bypass ported plenum, modified MAF (screens removed), edelbrock headers, hi-flo cat, flowmaster muffler.

 

DSouth,

I hope you used a reliable hand held tach to monitor RPM when setting the minimum air position. The factory in-dash tachometer is not really calibrated to be a diagnostic tool, and can be grossly innaccurate. Having to open the throttle stop screw several turns seems like a hint - possibly a bit too much adjustment. Make sure the engine is fully warmed when performing this adjustment.

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Later,
Vader
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"No matter how hard you try you can't stop us now"
Adobe Acrobat Reader 4.0

 

Vader,
I'm guilty as charged, used the dash tach. I have an old analog test meter with a tachometer. Can I use this on my TPI engine? If so, where do i hook up the postivie lead?
Also, what procedure do you recommend to check for vacuum leaks. I don't like the idea of spraying WD40 all around the intake for some reason.
As I recall, the vacuum reading was 17 at about 650 in neutral, but with the engine loaded in drive, it would drop down to below 15.
As always, thanks for your help.
DS

 

sounds like the TPS sensor isn't adjusted right either to me. It should be at .5 V at idle.

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'89 Formula 383 TPI

 

DSouth,

The analog meter will connect to the TACH terminal on the distributor cap or the distributor side of the coil primary, just like always. Getting the lead connected may take a creative adapter, but the tach reading should be accurate regardless of what is firing the coil. Just don't expect to get anything usefull out of the DWELL range on your meter unless you want to use it to check the relative pulse width on the injectors or to calibrate the enrichment solenoids on ECM controlled carbs (a dwell meter is nothing more than a duty-cycle meter).

17" vacuum at a low idle doesn't sound excessively low, but is at the middle- to low end of what I'd expect from your cam. I've got a similar Comp Cam with a little more duration in a 350 with big valves and ported factory iron heads holding 18" at a low idle.

And Greg is right. If you've moved the throttle position to adjust the minimum air, you need to recheck the TPS voltage. The change in throttle position will almost certainly change the sensor voltage at idle out of the desired range.

If you think you might have a vacuum leak around an intake gasket or plenum runner flange, mold some of your favorite color Play-Dough or plumbers putty around the suspect area. Play-Dough will eventually bake dry and crumble off without damaging anything, and plumbers putty will take a little brushing to get off, but either will stop a vacuum leak without seeping into the joint. It shouldn't be nearly as flammable as WD40 of carb cleaner spray.

Incidentally, a careful color selection of Play Dough can make your engine a fun place to play, too. If you're clever, you can take marketing photos and start selling the stuff to *****-boys as a power modification - anyone who would expect to get 20 HP gains from an empty coffee can will buy anything.

Seriously, if you have a choice, use white or light blue, since some colors can bake on to the aluminum intake and tubes, causing a permanent stain.

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Later,
Vader
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"No matter how hard you try you can't stop us now"
Adobe Acrobat Reader 4.0

 

Greg,
I checked and adjusted the TPS voltage to specification after adjusting the minimum air setting.

Vader,
I like the playdough idea. I'll have to put this an my christmas list.

What would cause the engine to fast idle after driving at freeway speeds and then coming to a stop? After about 10 or 15 seconds of fast idle (about 1,000 rpm), the idle will return to normal (550-600 rpm).