Rougher idle when installing stock plugs

[Zink57]

This is a weird one...
My TTA came with the GN plugs installed R44LTS instead of the correct (for TTA) R42LTS. I decided to go with the stockers due to the GN plugs being 2 steps hotter and thought that the colder plug would be safer and prevent detonation. I have noticed that the idle is rougher...and I was carefull to gap at stock .035 on all 6. I replaced the performance TTA chip with the stock TTA chip and the car idles a bit lower 750 rpm in "D"...but seems rough as compared to other 6s that I have driven. It seemed that the car idled smoother with the GN plugs and stock chip..then with the stock chip and stock AC Delco plugs being returned to stock. Has anyone seen this? Any experiences?

 

[MaxVO2]

A plug or some plugs themselves may be bad. Or, you might have damaged one of the plug wires when doing the swap.

Ohm out the wires, and check the plugs as well.

Also, you may have fueling issues that are causing the colder plugs to load up and foul, and the previous owner or person who worked on the car put the hotter plugs in to reduce the fouling during idle, etc.. and found the car ran better with them so he kept them in there rather than fix the root cause of the problem.

Obviously, the basics such as TPS, base fuel pressure, IAC, need to be in spec, along with having a chip matched to the injectors, and modifications on the car, etc.. The stock chip may no longer work well if the car has enough mods on it, even though the stock injectors are still on there. Also, vacuum leaks, or badly oil soaked plenum area from the PCV or a bad turbo seal can cause fouling and other issues like you describe if it is bad enough.

If you have scan tool data, post it, if you still are having problems with the stock colder plugs, and checked some or all of the stuff above.

Billy
Montgomery Village, MD

 

[TT/Ameasap]

It's probably the chip change you did. Try putting the old performance one back in and see if there is a difference. Remember to reset the ECM.Oh, post what scantool reading's you have and what chip.


Bo

 

[83ttypecooled]

rough idle

Hi!
Well, the worst I can think of is that my tta has a very rough idle, and I think it is generic to the car. Actually, I have noticed this on other 3.8s, notably the FWD 1986 Ciera. What do you guys think?

 

[Zink57]

Actually I don't have a scan tool. The car is 100% stock. The reason that I installed the original chip was that that I was getting obvious detonation at WOT @ 16.5 lbs with the race chip. The 91 octane in my neck of the woods sucks. With the stock chip the car runs better at WOT and idles lower. With the race chip it was idling in "D" about 900 rpms. I am thinking that the past owner might have installed the GN plugs due to the rarity of the TTA ones. I had to call 6 parts stores and eventually had to have them ordered (wait 3 days to come in). The car was just smogged and was one of the cleanest running 89s my step dad had seen (he's a mechanic)...he couldn't believe it.

The idle isn't all that bad...it just has a very very slight miss. I have heard that this idle problem is common with these cars on stock configuration. "P" it idles at 1000 rpm. "D" idles at 750 ish. Is that the norm?

 

[89ICBM]

This is a weird one...My TTA came with the GN plugs installed R44LTS instead of the correct (for TTA) R42LTS.


Howdy!

Your right. It is weird. GN plugs will not fit into a TTA head. The stock GN plug is a R44TS. Hopefully, using the hotter plug didn't do any damage. The stock chip does run rougher than most of the performance chips. The car needs a tune up and your going to need a scan tool to do it. Several things have to be set and can not be done with out a scan tool. The IAC needs to be reset, TPS voltage needs setting and the rpm in gear at idle. Go to this site http://www.89tta.com/. Click on tech then minimum air rate then the blue highlighted procedure.