1990 Grand Prix engine hesitation upon acceleration

[mp1642]

Attempting to diagnose engine hesitation upon acceleration from a stop on my 1990 Grand Prix 3.1 L.

Some quick info:
1. No CEL light on
2. Idle has been relearned after recent battery change ( Engine Starts and idles normal )
3. Recent replacement of spark plugs and ignition wire set ( I used AC Delco parts )
4. After initial hiccup from accelerating from a stop, engine runs nice ans smooth

Any help would be greatly appreciated..

[lefty1120]

Have you checked for vacuum leaks first? My '93 has a few questionable vacuum lines that I'm soon gonna replace.

[KX2000GTP]

Originally Posted by mp1642

3. Recent replacement of spark plugs and ignition wire set ( I used AC Delco parts )

Did the problem occur before or after plug and wire replacement??

If it was after, you might have gotten trash inside, or have a faulty wire OOTB.

What is the mileage, and have you replaced fuel filters or injectors at anypoint in the cars life??

Does it hesitate on every accel or only from stop? LIke if you were in traffic and punched it to get around the slowass in front of you, would it hesitate then?

[richtazz]

Inspect and clean (if necessary) the IAC valve pintle as well as the hole in the throttle body it rides in if they're carboned up.

[mp1642]

Sorry it took so long to respond to your questions. I will answer the questions in order.
And again......... Thank you for your help with this.

1. I have not checked all vacuum lines yet..... No hissing or idle lope noted.

2. The problem was occuring prior to the ignition wire set & spark plug replacement. ( this was done not as a fix but a maintenance item )

3. The current mileage is approx. 188,254 miles

4. Fuel filter replaced every 30-40k miles. Fuel injectors have not been replaced ( no problems ) since my ownership ( purchased with 140k miles )

5. The hesitation is more noted on accel from a stop. It does happen while accelerating from any speed. But again, most noted from a stop or lower speeds. It tends to be worse or most noticable when engine is cold.

Thanks again to all whom has responded and look forward to your continued help with this.

[richtazz]

The symptoms described in #5 above are classic IAC (Idle Air Control) motor problem. It's an electronic stepper motor that varies the amount of air allowed into the engine at closed and part throttle. If it is bad or carboned up/stuck, it will cause exactly what you're describing. here's a picture of the IAC from AC-Delco's website.

http://198.208.187.182/internet/View...umber=17112350

The cone shaped piece in the picture is what is inside the throttle body and is what get's carboned up