Another hanging idle...I've tried it all!

[mustanggt94]

Okay here's the story. I've had my car sitting with no engine and tranny for a long time now and I traded my bike for my buddy's 95 GT that he wrecked since he had a refreshed 306 and a new T-5 in it. Now when he had it in his car, it had the same hanging idle issue I am having. Here is what I have been doing to try to fix it:

1) Replaced IAC with a spare I have
2) Adjust the idle and TPS
3) While checking TPS voltage, I noticed a bad spot in the TPS, so I replaced TPS with new OEM Ford TPS
4) Hanging idle got better, but was still there after new TPS
5) Decided to readjust idle, but wanted to check the timing again....set the timing to 15 degrees.....now I cannot get the idle below 900 with the spout and IAC unplugged!! It's not that it dies, it's just that the idle screw won't go down any further! I noticed a slight hissing from the back of the motor....PCV valve hose was a little loose, seems to have too much pressure at the valve! Is it okay to have a direct vacuum line at the PCV valve? Anyway, I put a clamp on that hose but idle still too high.
6) Drove it around today and now the hanging is even worse, though the car pulls harder now that I bumped the timing! (for some reason the timing was under 10 degrees before)


Now here's the details:
1) When driving down the road, especially in 5th gear above 2000 rpm, when I let off the gas the car almost drives itself for a while, like the throttle is stuck. The revs slowly descend and once it hits 1900 exactly, then the rpms jerk back down like normal.
2) When slowing down, if I let the revs go to under 1000 before pushing the clutch in, then immediately after the clutch is pushed in the idle will actually go up to around 1300 or so and hang for a while before dropping down to around 900-1000 rpms (where it seems my idle is stuck at for now).

Here is what I have:
Stock block 306, no EGR hooked up (rigged valve so no MIL), no smog stuff, no cats...Trick flow intake, BBK 70mm TB, ProMass 80mm MAF, 30lb injectors, stock ECU..that's about all the relevant stuff.

So what do you guys think is next? Think the PCV valve thing is a problem? when I took the hose off the PCV valve there was so much vacuum it almost died. Can't remember if that is normal, been so long! Oh yeah and I didn't think you needed it in my case but I do not have any vacuum lines going to any of the canisters in the pass fender...is that a problem?

Please HELP!

 

[HISSIN50]

It sorta sounds like you still have a vac leak.

The idle hangs while rolling because that's how the puter is tuned. It keeps the car from stalling.

Have you ever considered one of those IAC block off plate things? A member on here (A.J. perhaps?) was selling/giving them away and some really had good luck. I never tried one and don't agree with setting a cold idle, but it might be something to consider.

Good luck.

 

[mustanggt94]

It sorta sounds like you still have a vac leak.

The idle hangs while rolling because that's how the puter is tuned. It keeps the car from stalling.

Have you ever considered one of those IAC block off plate things? A member on here (A.J. perhaps?) was selling/giving them away and some really had good luck. I never tried one and don't agree with setting a cold idle, but it might be something to consider.

Good luck.

Yeah I think I'll mess around with the vacuum lines this weekend, but most of the lines are new and I made sure they were all secure when I put the motor in. I'll probably go ahead and replace the PCV valve and maybe look into that IAC block off plate. I've read a little about them but I didn't think I'd have to go that far!

 

[Blackened302]

i was having the same issue after my engine swap, and i don't know what fixed it, exactly, but here's what i did:

1. bad iac--i overtightened it, broke it, so it was leaking
2. bad tps--tested and replaced (wouldn't move from 1.25 volts or something like that)
3. pcv valve was bad (didn't put a new one in during the swap )
4. vac leak from throttle body (re-used bad gasket )
5. vac leak at collector (right before the o2 sensor--misreading, running rich on one side)
6. BOTH o2 sensors were bad--replaced (went bad before the swap)

like i said, i don't know what fixed it, but i'm sure all those things were factors of a bad, surging, and hanging idle.

now, thankfully, car idles great--nice and steady w/ a slight lope from the cam.

good luck, hope that helps you some.