gsxranger

iTrader: (2)

I have an 87 turbo II, and yes I know there is war and peace written on the idle probs. The idle pulsed constantly when I bought it between 300-1000. After all general tune up stuff, and replacing all the vacuum hoses I could reach, it has settled in nicely at 650. It still hangs up for a split second at 900 on the way down, but I can live with that.

However, when I run the AC, or even the headlights for that matter, the pulsing returns. The AC particularly freaks it out, pulsing the idle up and down in a constant fasion. Anybody seen that before? The car is still completely stock.
Thanks
Jim

jjcobm

iTrader: (18)

The BAC Valve is used when the A/C is turned on. It basically allows air to enter the intake to compensate for the A/C load. If everything is fine up until you hit the A/C I would want to pinpoint the BAC as the suspect.

Make sure you have the TPS set correctly at 1v, then check the BAC valve located on the upper intake manifold....

satch

iTrader: (1)

I've had a similar problem in the past and while the culprit could have been this or that, in my case it was the throttle position sensor (tps). As stated above, check the voltage and hopefully you should be good to go. While your problem might relate to the bac it is easier to rule out the tps first as your problem and go from there. If you need the step by step procedure to check your tps just ask.

gsxranger

iTrader: (2)

I've searched for the TPS tests, it seems there is one that uses two test lights soldered together, one that uses two volt meters and one that uses one volt meter. Are they all equally accurate?
Thanks
Jim

satch

iTrader: (1)

The multimeter is an easy and accurate method. The fsm states the voltage output should be 1 volt on the nose and its easy to hone in to that value when and if the setting needs to be adjusted.

jjcobm

iTrader: (18)

If you have a multimeter handy, it is the easier way to go unless you want to take your time to make a test light. All give same results as stated above....

HAILERS2

Not arguing with anybody above..........when you select A/C, the ECU should have increased the idle rpms to approx 800 rpm (it's in the FSM).

Same when you turn the headlights on. You put a load on the engine....the engine idles a bit lower due to the Load put on it.....the BAC increases the air to the engine and the rpms pick back up to the 800 rpms.

Tell you what, if you get the engine fully HOT and idle it, if you pull the BAC's elect plug off, the engine should still idle close to 750 rpm. If it does not, then fix it so it does. That way when the BAC plug is put back on, and you then apply a LOAD to the engine with the A/C or headlights turned on, the BAC won't have to work if butt off trying to maintain a 750-800 rpm speed.

And I'm all for setting the TPS voltage output to one volt dc. Just make sure the engine is HOT when doing so. Probe the green/red wire on the plug that is ATTACHED to the TPS connector. The plug that is part of the EM harness, not the half of the plug attached to the TPS pigtail. You leave all plugs connected up when you do that. NOTHING disconnected.

A BAC elect plug that is half *** connected to the BAC's jack will cause the engine to *hump* up and down if the plug makes intermittent contact. Always a possibility.

jjcobm

iTrader: (18)

^Good advice

now that you brought it up let me also add that after setting the tps, you should also take the time to check your timing and make sure it is within the mark on the pulley and then set your idle to 750 as hailers mentioned.....

gsxranger

iTrader: (2)

Is the factory tach accurate enough to set idle with?

HAILERS2

yes

gsxranger

iTrader: (2)

Thanks everyone for the info - I looked over the FSM, is it such that the 1 V tests the function of the TPS and the double light set up allows you to adjust it?

satch

iTrader: (1)

There is a flat head screw which adjusts the voltage setting of the tps so all you need is the multimeter. The screw is found within a spring which is located just in front and above the tps.

jjcobm

iTrader: (18)

The 1v method is basically the same thing as the test light. If you had test lights hooked up they would light up around 1v while setting the screw next to the tps plunger. They are both the same thing with the same result.

You are only going to backprobe the "A" (green w/ red) wire (with a paperclip) and the black multimeter lead will go to your battery ground, this will give you the voltage readout (this is off s5, you might have to play with your, either a or b, since its an s4 unless the wire color is the same):

http://howto.globalvicinity.com/gv_w...i=58&co=1&vi=1

You then use the screw next to the plunger to adjust the voltage to 1v on the multimeter.

Make sure to fully warm up the car before you do this, then check your timing, then set the idle to 750.

gsxranger

iTrader: (2)

Thank you everyone for your input. I went to do this last night and it was "interesting"

My car is totally stock, and I don't think anyone has turned a wrench on it in 15 years, just changed the oil. The TPS was reading .66 to start, I had to turn the screw 4 whole turns to get it to 1.00 Whenever I am "fine tuning" something and I have to make big changes like that, I start to feel uncomfortable.

Next I checked the BAC valve by disconecting it, and the idle dropped immediately.

I don't have a timing light, so I gotta try and borrow one this weekend.

I plugged the BAC back in and moved on to set the idle, jumped the green connector behind the headlight. Idle was sitting steady at 600. Not sure which way to turn the scew for faster, I started turning it out. After about 4.5 turns, it looked like it wasn't making any difference, just up about 75 rpms, so I tried in. After about 8 turns in it finally dropped to 500. Backed it out as far as I felt was reasonable, but still couldn't really top about 675. ???

However, the surging idle is considerably better. It will surge once when I turn on the AC, and then seems to find it's equilibrium. After it got really hot yesterday, it did surge again for a while. The whole car seems to run a lot better in lower RPMs, and the transition is smoother. Next up is the timing, I was just suprised how far I had to turn these screws.

jjcobm

iTrader: (18)

try to set the idle with the BAC disconnected like mentioned before. The screw is a bit odd sometimes for the idle, it is quite possible there dirt inside the throttle body passages that is why you are not experiencing any difference. You can try to take out the screw completely and spray some carb cleaner down the hole, but the best would be to take out the four nuts that hold down the TB, remove it, and clean it from there.....

For setting the TPS, did you make sure to fully warm up the car before doing it? In case you didn't, it will give you inaccurate readings....

gsxranger

iTrader: (2)

I'd like to but turning the BAC screw at this point seems to have little or no effect on the idle. I got the timing set yesterday, it was just off a smidge. I'm going to try to remove the screw from the BAC and spay it out with cleaner. More and more I'm beginning to suspect the BAC valve, even though it passes the pull the plug test. (idle drops when I pull it.)