My 1987 Mercury Colony Park

[DerekTheGreat]

...FWIW, it did point to engine idle speed being possibly lower than what it should be. I was getting, high idle at ~850RPM, ~600 in Park after stepdown, and ~450 in Drive. Engine sticker indicated Drive idle speed should be 525-650 range. This may all come back around to me having to adjust the stop screw on the throttle body after the intake swap since I couldn't get the TPS in range. I may need to index the TPS's ears a bit for more adjustment so I can the idle speed square and keep the TPS in range. It may also explain why during a KOER test with the old IAC I was getting a RPM High Limit Not Reached. I'll be pleasantly surprised if that'll let me get things dialed in.

The idle speed is controlled by the ECM, so if your IAC is 100% open and still not able to get idle in gear up to where it wants it to be I could see that being feasible. However, didn't you verify TPS is in range? That's something to be mindful of when changing the factory curb idle, as messing with that might put you out of spec. I've heard of IAC motors being dead, and with these things unless you back probe sensors or have a break out box you won't know if it's responding to input from the ECM. I talk about Ashley's '92 F150 a lot, and being able to see what the commanded position vs actual position of the IAC motor is really nice, amongst other things I was previously blind to. Stinks that Ford took so long to get to the "free market" table. GM was there in '87....

[Kodachrome Wolf]

The idle speed is controlled by the ECM, so if your IAC is 100% open and still not able to get idle in gear up to where it wants it to be I could see that being feasible. However, didn't you verify TPS is in range? That's something to be mindful of when changing the factory curb idle, as messing with that might put you out of spec. I've heard of IAC motors being dead, and with these things unless you back probe sensors or have a break out box you won't know if it's responding to input from the ECM. I talk about Ashley's '92 F150 a lot, and being able to see what the commanded position vs actual position of the IAC motor is really nice, amongst other things I was previously blind to. Stinks that Ford took so long to get to the "free market" table. GM was there in '87....

The TPS is in range, however when it was first installed on the HO TB, it was way out. I asked the guy I got it from if anyone messed with the stop screw and he said no. His Mustang ran fine, didn’t idle crazy high. The IAC definitely works to get the idle up and down, but it can only make so much adjustment.

What I can do is index the ears for greater adjustment range and give that a try when I “reset” the idle screw.

[Kodachrome Wolf]

Going based on StangNet and their surging idle check list, it said to ensure the engine could idle roughly at 600 RPM with the IAC unplugged and SPOUT out. I was idling closer to 300 on a warm engine and it wanted to shutoff. Bumped it up to 600 RPM and took the TPS off and widened the holes a bit and reset it within range, then plugged back up the SPOUT and IAC. Now it starts up and holds around 625 in idle and roughly 585 in Drive. Going to take it out and see how it does.


Edit: Does run better, idle isn’t stumbling in Drive when warm after being driven. The tach needs some attention, it’ll respond great with slow engine speed changes but doesn’t respond to fast changes. Went WOT and it barely climbed up to 3000 before the car shifted into the next gear. Might just be a connection issue.

[DerekTheGreat]

Hmm, it didn't occur to me to trim some of the plastic on the TPS to achieve desired results.

Didn't you say that tach was sitting for years? It could just be corroded on the inside, especially if it likes to read accurately below 2k or so. Over ten years ago some friends and I had either stick shift Rangers or F150's, the ones with F150's never took their stuff above 2k rpm's. Silly thing was they installed aftermarket tachs when patience and a few junkyard visits would have netted them with a factory tach which requires zero modification or wiring to add to the truck..

[Kodachrome Wolf]

Hmm, it didn't occur to me to trim some of the plastic on the TPS to achieve desired results.

Didn't you say that tach was sitting for years? It could just be corroded on the inside, especially if it likes to read accurately below 2k or so. Over ten years ago some friends and I had either stick shift Rangers or F150's, the ones with F150's never took their stuff above 2k rpm's. Silly thing was they installed aftermarket tachs when patience and a few junkyard visits would have netted them with a factory tach which requires zero modification or wiring to add to the truck..

I just didn’t have enough adjustment with the factory holes. I didn’t have to enlarge them a whole lot, just enough for some extra rotation.

As far the tach goes, who knows how long it was stored out of use. It barely reads outside of 1000. There might be a reason it was sitting in a box collecting dust. It’s a no-name unit likely from the ‘70s. Figure swapping it for a new one wouldn’t be a bad idea, plus a 2-1/2” unit would be a bit more suitable for the placement anyway.

[Kodachrome Wolf]

Pro Tip: Don't base engine idle speeds off a tach with questionable readings. Popped in a new replacement that's worth a damn, and it's idling at 1000 in park. That needs to come down some.

FWIW, it's almost in range according to the emission label under the hood for vehicle in gear. It's sitting roughly 50 RPM above 650. ¯\_(ツ)_/¯

[DerekTheGreat]

Haha, yeah I did that once. I was trying to adjust the idle on Ashley's '88 C3500 with a 454 by using the factory in cluster tach. Tach read about 900 or 1000rpm's where as the Snap-Off MT2500 reported 800, right where the damn thing wanted to be. I won't admit to how much time I wasted doing that haha. My one friend had this to say after the fact when he heard the story: Most old guys go by ear. Well, come to think of it, it did sound right but because the factory tach didn't read right my panties got scrunched. Lesson learned.

The idle speed when in gear is a weird thing, and I highly recommend adjusting for that vs idle speed when in park or neutral. I had that battle with my '85 LTD. Idle ended up being slightly higher than Ford specified when in park but in gear it was spot on, which was better when in stop & go as it wasn't rough any more.

[gadget73]

Target idle is 672 rpm IIRC.

Gauges are often somewhat out to lunch if they aren't fancy expensive ones. After a while they become more of a reference than an exact measurement. Needle "here" is right, anywhere else is wrong, no matter what the scale behind it says. Most of the time thats good enough, when it isn't you spend actual money and buy better instruments.

[DerekTheGreat]

Yep, and when I plugged in the MT2500 I was like "Oh, it is correct." I admitted my shame to Ashley.

[gadget73]

The boat my folks used to have was twin V8 powered, so two complete sets of instruments and a "sync" gauge that is used to match rpm on the engines. If its in the middle, they run at the same speed. You can also hear it. One tach read some 200 rpm higher than the other even though the engines were in sync. The lower reading one would start out the day some 600 rpm high until it got a Fonzarelli on the dashboard, then it would drop back to where it belonged. Never figured out either problem, just learned how to live with it. Initially both read way off, the factory-installed tachs were set for 6 cyl use instead of 8. Fixing that made them read sane rpm but I wouldn't have trusted either further than I could have pitched them overboard.

[DerekTheGreat]

Hey look, they're called indicators and both were indicating. Engine speed? Yes. What more do you want? /s

A Fonzarelli, LoL. Haven't heard that in awhile.

[gadget73]

That boat had a few things that needed the occasional whack in the right spot to make it go. Never figured out any of them, I just learned where to hit them.

[Kodachrome Wolf]

Decided to order replacement catalytic converters for the car. It truly is awful parking it in the garage if I don't let it air out for a few minutes from the fumes.

I ordered Magnaflow units through work, got both units for right under $180. Compared to how the factory setup used two per side, these new ones only use one per side. Hopefully I don't run into any issues running without the Thermactor system in place, but I figure it's worth a shot.

[sly]

It actually has two cells, but in the one chamber. The first in the front third and the second in the rear third of the chamber with the middle third meant for the air injection. The original style had one cell per chamber with the air injection in the pipe between the chambers. They are MUCH easier to mount than the OE stuff too. That's exactly the stuff I used for both the Mad Marquis and the Cake.

[gadget73]

Even if you get new direct fit stuff its generally going to be the 2 cat pipe rather than the 4. The Fox H pipes are that way.