Problem at WOT, idle issues


Well-Known Member
Feb 15, 2003
Just some quick questions for the experts out there....

Finally got around to tuning the '86 T I just bought. I've noticed that at WOT the cars skips a little bit. My first thought was ignition related, or possibly fuel related. I'm running 100 Octane and around 19lbs boost.

I hooked up Turbolink and took some idle readings and cruise readings. I tried to do some WOT readings but its almost impossible in this weather unless I was on the freeway doing about 70. O2 readings bouncing around like normal and seems fine.

I then checked the fuel pressure and noticed it was set at 50psi with vac off! I turned it down to 43psi or so and took it for another spin. It started to snow just a little so I couldn't tell if it had any effect. Never saw any knock except for a little on wheel spin (at about 50mph heh). I won't be able to tell much until I can WOT, but I'm assuming the 50 was way rich. Could this lead to the skipping at WOT I had experienced previously?

I've noticed the idle bounces a little and even more so now that I turned the fuel pressure down. Looking at the numbers at idle, I noticed the TPS is at 0.47 (a little high but within range) but the IAC is steady in the mid 50's. Would this cause my idle to bounce around like it does? I assume the solution is to adjust the IAC to 20-25 and then adjust the TPS accordingly.

You want your TPS between .44 and .46. IAC at idle in Park should be between 10-30. I'd check your coil pack first for the WOT issue. Running rich shouldn't cause your car to "skip". WOT problems could be anything... i'd start with easy simple stuff and work from there. Coil pack, plugs, wires...ect. When i first got my GN the stock cam had a wiped out lobe which caused it to surge and knock like a SOB at WOT.
Thanks, thats the info I wanted about the skip. I plan on changing all the plugs, plug wires and coil this week with all Delco stuff. The skipping isn't very bad, so I'm hoping it isn't anything serious. After that, I guess I could look at the injectors and change the fuel filter.

I'll do the IAC and TPS in the next day or so. Looks pretty easy with a scan tool such as Turbolink. Hopefully that will cure my idle problems. If that doesn't work I'll look at changing the IAC and checking vacuum lines. I checked quickly but didn't see anything, plus its cold outside and I don't have a garage.

I'll update everything in a few days.
Well, got the idle issue under control. IAC now at 22 and TPS around .46 with 4.80 at WOT. Idles nice and smooth now.

I used the gnttype page for adjusting with a scan tool for the how to. One thing that may help others was that since my initial IAC was way off, turning the screw made my TPS go up enough so that the car was now out of idle (> 0.50). The IAC readings started fluctuating alot when this happened so I then reset the TPS back to 0.43 or so to get it within range. I had to go through this twice before I was able to get the IAC within range and a nice smooth idle.

Next will be to get the "skipping" at WOT under control. I will replace the plugs, plug wires and coil pack over the weekend as good measure, along with the fuel filter. I will also change the chip to a Thrasher 92 made for my injectors. The current chip in it is made for 28lb injectors and I'm sure doesn't help matters, but the previous owner had no problem with it that I know of.

I've also got a RJC Powerplate, new K&N, and Art Carr transmission cooler to put on too. Should be in good tune shortly. Since I have a Sunoco GT100 station nearby, I may get a Thrasher100 or RA100 chip or have one customized for even more fun. ;)

I think I've got the reasons for the skipping at WOT now and solved most of it.

As mentioned before, the car has a chip in it for stock injectors even though it has blue tops. I have a Thrasher 92 for it, but wanted to put my test pipe back on first since I just bought a new cat for emissions.

The car has an ATR fuel/air ratio meter (always says rich :p ) and there was some thing under the hood with lights that I thought was for the ATR meter. After tracing the wires, turns out its a TPS enhancer. I noticed this when adjusting the idle, but left it alone.

After some thinking and understanding what the TPS enhancer does, I decided to unhook it and see what it did. I had the laptop hooked and noticed a slight drop in TPS voltage at WOT, but thats what I expected since I do have the floor mats in.

What the TPS enhancer does it set the TPS voltage to around 4.8 volts (on my car) when the throttle is only at 66%. Makes for easier tire spinning and maybe a quicker surge at less throttle. Supposedly its for better throttle response.

Well, using the TPS enhancer combined with a chip for stock injectors, I think my car was running way, way rich as soon as the TPS enhancer kicked in. This caused my car to skip, etc at less than WOT but ran normal besides that.

Unhooking the TPS enhancer, the car now runs great and has better throttle response, or should I say more predictable throttle response. I still notice a small skip now and then when at WOT (but not at 66%, 80% or 90% WOT). I'm assuming this is due to the chip being for the stock injectors making it run too rich, but not as bad as before.

I'm in the process of putting the test pipe and Thrasher 92 chip for blue tops in and I hope the skipping will be gone completely. I have new plugs, plug wires, and coil but have not put them in yet, so it wasn't due to any of those things.

Just thought I'd update and give the info for anyone having a similar problem. (For any of the experts, does my reasoning seem right?)

TPS enhancers are no good. A volt booster is a much better product. I'd do the plugs, wires, and test pipe and see how it runs. Make sure you gap the plugs to .035 and use copper ones, not platnum.