1993 L idle rpm spontaneously goes too high -- on the road

[AlaskaFestivaGuy]

My East coast Festy, a 1993 (obviously FI'd) is acting like it has a wacko carb here in Pittsburgh. The RPM spontaneously jumps about 500rpm (no tach to measure) for a few minutes, then spontaneously returns to normal. Periodically, the orange engine check light illuminates for about 3 seconds while in motion. I don't feel comfortable driving anywhere but the slow lane, fearing what it might do/not do next.

I'm guessing this is some sort of sensor problem or maybe a deranged ECU. With all my Festies (about a dozen), I've NEVER seen an RPM problem in a FI'd car!

I don't have any spare parts with me, certainly not sensors or spare ECU. A few shops I've stopped by have blown me off with statements like "Too old" and "What's that you're driving?"

[WmWatt]

Check all vacuum hoses for loosness or cracks. The transient code you are seeing will be stored in the computer until cleared. Do you have your Haynes manual with you?

[AlaskaFestivaGuy]

WmWatt,

That's for your 2 a.m. response! Here's my 3 a.m. response to your response …

Vacuum hoses? This is fuel-injected, not carb'd -- are there any vacuum hoses at all?

What do you mean by "transient code you are seeing?" I didn't think Festies, even FI'd ones, had the OBD diagnostic stuff. Or …. is the momentary "check engine" light trying to tell me something? Is it "pulsing"" out some sort of code number? If it does have OBD, could I go to some McParts place and have them plug in a code-reader (or sell me one) to get a code? There's an AutoZone down the street from where I'm working.

No, my only Haynes manual is up in Anchorage.

My guess -- just a guess -- is that some sensor, such as throttle position or rpm, is intermittently giving out goofy data, so the ECU is trying to keep the car running by idling at what it considers some "mid-range" power setting, Kinda of like when an airplane's airspeed indicator fails, a smart pilot will set the flight and power controls to get some normal/safe configuration, neither stall nor overspeed. If that is the case, could I just install a couple of replacement sensors and sort the details out when I get home in weeks/months/whatever? I did a search and found terms like TPS, VAF, and others.

[AlaskaFestivaGuy]

FWIW, the problem seems to have suddenly started a few days ago when I did my first fuel fill-up (8.5 gals) at an off-brand gas station since arriving here 3 weeks ago. Perhaps I got some bad gas and the ECU is struggling with it?

[firebush357]

The car has an OBD1 system for the check engine light which requires you to jump some connectors near the brake booster and cycle the key on and watch how many times the light flashes long and short flashes and use that info to decode the issue. I doubt that bad gas would cause it to idle up like that. My first suggestion would be to unplug the Engine Coolant Temp Sensor on the back side of the engine and see if that helps. I believe that it has a green connector and comes off of the same harness as the fuel injectors and thottle position switch. If that fixes the issue then just replace it or run with it unplugged. It will run rich when unplugged though.

[WmWatt]

My engine coolant temp sensor was turning the check engine light on and off last winter but there was no noticable change in engine rev's. Mine's carburetted.

To read the code on a '93 Festiva connect the one pin white connector near the brake booster to the ground pin in the white 6-pin diagnostic connector and count the flashes of the check engine light when the ignition key is turned on. It doesn't show which terminal is ground but maybe the black wire?

[AlaskaFestivaGuy]

I have an appointment tonight at Napa here to plug in their OBD-1 reader. Autozone only has OBD-2 and doesn't even sell OBD-1. They say everybody traded in their 1's for 2's years ago.

Inside of tailpipe is black, so may be a mixture/whatever issue.

I hope to have a code in about 6 hours!

[AlaskaFestivaGuy]

The 6-pin connector (which is black) has 3 positions occupied and 3 vacant. I can't see wire colors where it goes into the harness. Which pin is ground? What's on the white single-pin connector? Will it hurt to try jumpering it in turn to each of the 3 occupied positions on the 6-pin connector? I don't want to risk frying anything here.

Napa lied to me -- they don't have an OBD-1 reader. I tried another AutoZone, which sold me a brand new Ford-specific ODB1-only code reader, but it used a different set of 3-of-6 pins than my connector has and its list of many covered Ford vehicles did NOT include Festiva or Aspire. I tried it anyway and got nothing.

I also stopped by a giant Ford dealer, where everybody just laughed when they saw what I was driving. It took quite a while to get RPM up above 200 (yes, two hundred) to get out of there. So the problem is getting worse quickly. Or maybe whatever's coating the inside of the tailpipe with soot is damaging the engine in some manner?

My best bet seems to be to try the jumper thing but I really want to know what's on the single-pin white connector. If it's NOT "hot" (i.e. if it's just a digital signal), them I'm probably safe jumpering it to each of the 3 pins looking for a score.

[firebush357]

So the 200RPM issue, did it start when you first started driving the car around or did it start once it warmed up? If it started after it warmed up it could be the Idle Air Control Valve getting stuck.

I don't think it would cause an issue jumping to any of those 3 pins since it is just trying to close a circuit. If you go to the Facebook Group there are PDF versions of the manuals that you can download. Since these are Mazda engines they may require a Mazda obd1 reader but I can't tell you that for sure, most people just jump the wires and read the dash light.

Is the car constantly down on power or is the issue intermittent?

[WmWatt]

Addendum: The Haynes manual says to ground the STI (the one hole connector) to chassis ground on the carburetted models but to the GND pin on the 6-pin connector on the 90-93 models. As I have the carburettor model I clip the wire to one of the posts on top of the strut tower. I don't know why you have to ground the STI pin on that specific ground wire for the early EFI models. Good luck. BTW like you I am very reluctant to connect wires randomly.

[WmWatt]

It occured to me that the STI connector has to be grounded when setting the ignition timing so looking at those instructions in the Haynes manual it just says connect STI to GND which must mean chassis ground as no GND connector is mentioned.

Returning to the diagnostic section only the STO pin is labelled on the 6-pin connector diagram and that is where to connect a voltmeter if using one to read the codes. The accomanying "EFI systems through 95" text reads "Simply ground the STI and GND terminals with a jumper wire and watch the light on the dash as it flashes the stored trouble code(s)." The test connector on the 89-93 EFI models differs from the one on the 94-95 models. The latter has a GND pin labeled in the photo. The text is for both which is probably the source of the confusion. So I would assume the STI connector could be connected to chassis GND to read the codes on a 93 EFI. If it were my car would go ahead and ground to the chassis to read the code.

BTW I did a Google search on "93 Festiva diagnostic connector pin-out" without success. You may have better luck with that.

[AlaskaFestivaGuy]

The problem doesn't start until the car is partially warmed up -- about 7 or 8 minutes of 35mph driving. It starts stumbling climbing steel hills once fully warmed up. After cooling down, the cycle repeats. I don't dare go out on the freeways (and don't really need to).

O'Reilly here offered me a $229 Bosch "V1/V2/everything" kit. Upon inspection, it lacked anything that would connect to the Festy 6-pin connector.

I visited several "old fart mechanics" today to whom I was referred with the assurance that they had V1 tools with Festy connector. None did. I'm visiting yet another one Friday 8 a.m. who told me on the phone that the white 1-pin connector itself is ground, implying that connecting it to the frame will do nothing, but connecting it to a pin on the 6-pinner might do something (good or bad).

If still unsuccessful by COB on Friday, I'll look up schematics as suggested here and fiddle with it from my hotel this weekend.

[WmWatt]

Warming up problems could be the ignition control module They are sensitive to heat and cause intermittent problems when deteriorating.

The car runs in open loop mode until the O2 sensor warms up and starts sending a signal at which time the computer takes over along with all the emissions devices but it shouldn't take that long for the O2 sensor to warm up. Maybe you could try unplugging the O2 sensor and see if the problem goes away.

[AlaskaFestivaGuy]

I know ICMs! One of my LXs would abruptly stop running after about 20 mins, then run perfectly again after a half-hour, due to what turned out to be a bad ICM (which cost about $200 just for the part) inside the distributor. But I thought ICMs were only in carbed Festies!

O2 sensor sounds like a leading suspect -- where is it located?

I'm two hours away from my 8 a.m. hopefully-for-real-this-time meetup with an OBD-1 tester!

[firebush357]

The 02 sensor can be unplugged at the connector that sits between the radiator fan shroud and the distributor. The O2 sensor is mounted on the down pipe in front of the engine and should have a single wire running to it that clips onto the heat shroud for the exhaust manifold.