Jester

I'd like to start by mentioning.... I am a dumbass, so bare with me here....
Ok, sometimes my car is hard to start but I'm pretty sure thats just cause of flooding because when I flip the switch to shut off my fuel pump and crank for a while, it will turn on, so I don't think thats a portion of the problem. Lots of times though, my car has a problem stopping where it should idle. In other words, when I'm comming up to a stop and I take the car out of gear, my rpm's drop really fast and fly right past 750 (ideal rpm spot I think). It usually drops to like 250 and bobs between 500 and half the time it won't be able to hold and it will die and the other half of the time, it will recover and come back up to 750. It is especially bad when I have the AC on. I was wondering if anyone could tell me what could be causing this. I donno what the difference between the TPS and the IAC is really but I'm assuming that both of those could be a problem.
Another thing, you can get a fairly accurate reading of what you compression is with a normal compression tester, right? If the needle jumps to 30-60-90 and then creeps up to around 100, its doing what its sposta right? And is 100 good for a '87 TII? Thanks for all the help!

Fritz_X

iTrader: (1)

http://1300cc.com/howto/how2/bac.htm

Good luck there!

--Fritz

WAYNE88N/A

30 60 90? Are those the pulses with the check valve in the gauge? And 100 is total?

Take the check valve out, and crank her again. You should get continuous even pulses on the gauge of something between 85 and 120 or so. If she's showing 30, 60, 90 over & over, you've got problems...

Jester

I found that website after I posted this and it sounds like a deal. However, it says a way to test if this is the problem is to run your car and turn on your heater and see how long it takes to recover. Well, when I turn on my heater, my rpm's barely drop (like maybe 100 rpm's) and I don't know if it ever goes back up. However, if I turn on my AC it drops like 500 rpm's so is this the same test?

As for the compression testing.... man, it was over a year ago but if I remember right, when we cranked the car, the needle juped to 30 then to 60 then to 90 and then it just made little jumps on up to 100 total.

WAYNE88N/A

Sounds like you had the check valve installed then, no biggie, except that the numbers sound kinda low. You'll have to perform another compression test sooner or later if the BAC checks don't solve anything.

Speaking of BAC checks, I've found that the easiest way to test this sucker to see what she's doing is to get a volt meter and probe the BAC "output" pin to ground at the ECU (pin 2Q on the S4 cars, last upper pin on the left of the middle plug, with it connected to the ECU). Just keep the meter on, and drive her around for a little bit, putting different electrical loads on her. When you get to a stop and she's idling, you should see the voltage drop from 11-12v to 8-9v- that's the results of the ECU switching the ground on & off at about a 30% duty cycle, to energize the BAC and allow bypass air into the intake system. The voltage will fall lower & lower as more electrical loads are applied (should fall at least 1 to 1.5v with the A/C switched on, I would think). If you see no voltage drops whatsoever during loading, your BAC system is shot (although at this point you know the wiring is good, or no voltage at all would be present at 2Q)

Jester

Could it still be this if it happens even when my AC isn't on? Because it does it a lot when the AC isn't on, it just seems to be worse when AC is on. However, tonight was kinda weird, I drove w/ the AC on and didn't have any problems, but thats extremely unusual