High idle issue

So quick background. Installed new blower, injectors, fuel pump, c&l maf, bbk 70mm tb, and QH with Dalke base tune. Also egr delete. Like an idiot I lost my usb dongle license for binary editor so I don't have full visibility to what's going on yet. Hopefully that will shed some light. In the meantime, here's what's happening.

The car started right up first try and sounds healthy. Idles at around 1500 rpm though. After checking the tps voltage I have 4.7v for reference but zero for signal.... When I unplug the IAC it dies back down to 5-700 with a tendency to stall but it will run. Checked all connections with propane with no changes in engine speed so I don't think I have a vacuum leak. Throttle adjustment screw is backed out all the way and then turned in about 1/4 turn - blade still reports a crisp metal on metal closing action. Idle bypass screw is closed all the way.

Until I get licensed again for binary editor, any suggestions or thoughts? I could pull codes with my scanner but I don't like running the car blind right now.

Not sure a propane check is helpful if the computer responds faster than expected to smooth things out. Might want to pressurize the intake tract instead.

KMT said:

Not sure a propane check is helpful if the computer responds faster than expected to smooth things out. Might want to pressurize the intake tract instead.

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So you're saying its all symptomatic of a vacuum leak? It's pulling a hair over 20" hg. I just don't see where the leak could be though, I was meticulous with Teflon gaskets, rtv and proper reassembly. How would this explain the 0 v from the tps? It's almost like the EEC is sending a signal for the IAC to stay open and I don't know what would cause that?

BUDXR7 said:

So you're saying its all symptomatic of a vacuum leak?

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No, just politely questioning your methodology

How would this explain the 0 v from the tps? It's almost like the EEC is sending a signal for the IAC to stay open and I don't know what would cause that?

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Remember, TPS is referenced as a range/swing, not so much a hard coded spec.

To me it sounds like the IAC is generally working properly, assuming no vacuum leaks there, of course (did you inspect it's insides latery), so maybe the EEC is acting out - perhaps bad grounds? Leak at the throttle plate shaft (and why are both the bleed/bypass screw and plate shut)? Unmetered air after the MAF? Contaminated MAF? CAI oiled recently? What happens if you disconnect the MAF and try to start?

Here's an update. I ran the car with the MAF unplugged and the idle dropped to about 850 but it didn't sound good. Side note, its running rich judging by the exhaust smell. So I plugged the MAF back in and ran the code scanner. KOEO gave me 63o, 63c, and 66c. These point to the TPS and the MAF. I think the 66c was from me unplugging the MAF while running. The engine failed the KOER test , code 98, and threw another 63, TPS again. The car is basically running in "safe mode".

So I pulled the throttle body off to get at the TPS (god damn ford engineers....) and remove it. Side question, is there a gasket that goes between the sensor and the throttle body? It wasnt on the stock TB so I didn't bother on the bbk. On to my test. From the top down the pins in the TPS are labeled a,b,c. From the top down the wires in the plug are black/white (ground), green/green (signal) and orange/white ( reference). To my thinking, there should be resistance between signal and reference but not overload (open). That would be pins b and c. When I measure it I get overload as though the circuit is open. It doesn't change when rotating the sensor. There is resistance between ground and reference, which I would have expected to be open. Don't know what that means.

Anyhow, I'm thinking a new TPS is in order. Thoughts?

If that TPS is original, I wouldn't waste too much time w/it - investing in a new one is in your best interest, I think.

If you're really curious, repeat your testing on the new one to see it if acts differently (I think it will).

KMT said:

If that TPS is original, I wouldn't waste too much time w/it - investing in a new one is in your best interest, I think.

If you're really curious, repeat your testing on the new one to see it if acts differently (I think it will).

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Yeah, on order. I may not have been as gentle with it as I should have been. I'll follow up with the results in hopes that this will serve somebody in the future.

I'll follow up

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That would be good, thanks and good luck.

Ken

I received the new TPS. I checked the resistance between pins b and c and I got 138 ohms. So OL is sure sign of failure. One take away from this, test it before you reinstall your throttlebody. It's a majors ~~~~ to remove the throttlebody and sensors from the inlet plenum. In fact, as long as you don't have EGR, it's almost easier to remove the whole blower to get at these sensors. Crazy but true.

So I now have .59v for signal, which seems a bit low so I guess I'll be adjusting it now.

Don't bother adjusting it as long as it responds smoothly with throttle input.

FWIW Ford doesn't have "limp mode". When a sensor is bad it uses a preset default for that sensor and carries on like normal as much as possible.

Also, a vacuum leak will not cause low vacuum on your dash gauge unless the leak is crazy severe. Most leaks are compensated for as KMT indicated much faster than you can observe so propane and other "fuel" based leak detection techniques are 95% ineffective. But I'm going to assume at this point that you found your problem already.

XR7 Dave said:

Don't bother adjusting it as long as it responds smoothly with throttle input.

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I didn't drill anything, loosened the screws, tweaked ever so slightly, retightened, and now I get a smooth transition from .71 to 4.35. I'll be reassembling later to see how it runs. Thanks guys.

BUDXR7 said:

So I now have .59v for signal, which seems a bit low so I guess I'll be adjusting it now.

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As I said above...remember, TPS is referenced as a range/swing. No adjustment needed as long as it's basic function is being served, and why these units don't provide adjustment like TPS of old.

Stock acceptable range for TPS initial position on 89-90 SC's is .575v-1.175v Anything in between those values will not set a CEL. Minimum recognized TPS initial value is .4v which means it will work, but will set a CEL if between .4v and .575v. Below .4v the EEC will disregard TPS voltage and running issues will result. These can be adjusted in the tune, but those are the stock values. All other references to TPS in the EEC programming are base + some value, they are never absolute values. The EEC re-learns base TPS every time the key has been turned off for at least 10 seconds. So if you jack around with the throttle stop screw while the engine is running, things can get goofy and you may need to shut the engine off for 10 seconds so it can relearn your adjusted value.