Lance A

My car is a 1986.5 AT. It has new plugs, wires, O2 sensor, intake boots, MAF boot, and the vacuum lines have been tested with the mityvac. I have also cleaned the idle control valve, and the MAF. The car still requires gas to start, hunts for idle, and if you back off the gas too quickly the engine will die. It is also running rich. What else is left?
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black 1986.5 AT

FeedNfrenZ

I had the same issue with my 85. I wish I could tell you exactly what fixed it but what I did was an intake rebuild. Pulled the intake, new gaskets, vacuum lines and hoses, after reassemble the problem was gone.

Landseer

Mike Frye has been painstakingly addressing all kinds of intake issues here for the last few months on an 85 (same as your intake). I'm sitting here reviewing his posts this minute as I am refreshing one this afternoon myself. You might want to search through his posts, maybe advance search, and I'll bet you will turn-up some assists. Some of his targets were setting the TPS and assessing the idle control valve and replacing the O-rings on the butterfly valve on the throttle body. Also, lots of tuning references.

He says unmetered air is a culprit of idle hunt.

Mike Frye

Hi Lance,

My money is on the O2 sensor circuit. I know you said the O2 sensor is new, but if you unplug it is there any change? If not, then there's a problem with the sensor or the connector. If it's happening mostly at start up, I'd guess probably the O2, otherwise it may be unmetered air as Landseer points out.

I had a hunting idle at startup (hot or cold) that didn't go away after I replaced the O2 sensor, and finally found that someone had pulled on the wire at the plug and made for a bad connection inside the wire insulation at the plug. Once I replaced that, the idle smoothed out.

I'd recommend going through the entire idle test plan from the WSM that starts with setting the CO at the MAF (you can do this with the 'Blink'r' that Porken makes) and then move on from there.

Edit: Landseer, 'painstaking' is a kind way of putting it. You know what they say, 'If you're gonna be dumb, you better be tough.' Or in my case, persistent.

Imo000

Did you set the base idle?

Lance A

Imo000-
Forgive my ignorance im still new to 928 ownership and RL. By base idle I assume you mean setting it to idle at the manufacturer spec of 700 rpm (cant remember exact) I have not set it but after hunting for idle for a while it levels out at the correct RPM. Tomorrow i plan to go through the WSM and perform the idle test plan like Mike suggested.
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Black 1986.5 At

Lance A

Mike-
There is no change in the way the car runs with or w/o the O2 sensor hooked up. I checked the plug connections on the car, and they looked fine. But with my luck the problem could be the main connection to the circuit board. Any thoughts?

Mike Frye

AH, that's the way it worked for me. I suppose it's not a conclusive test, but the fact that it surges upon startup (does it do that hot and cold, or just hot or just cold?) and then settles down to a good idle indicates to me that it's not an unmetered air problem (or vacuum leak).


The lead that comes from the O2 sensor is 3 wire, the two blacks are for the heater (this may be the problem, causing it to not heat up initially, but then after the car warms up the O2 it starts working OK> car idles OK) or it could be the green wire that goes into the rubber plug. You can try metering these before and then through the plug, they're only a single conductor AFAIK.

The green wire has a center conductor and a shield to cut down on signal interference but the shield isn't part of the circuit when it's plugged in. What you'll notice about that plug is it's like a Chinese finger trap. The more you pull on the base, the tighter it holds on and if someone just yanked on the wire it probably disco-ed the center conductor from the plug. This is what I guess happened to mine because when I wiggled it, it would change the startup idle.

I cut the plug out (male and female) and soldered a new set on there so I've got a solid connection.

IMO000 is talking about setting the base idle as you described according to the WSM, which is part of the test plan I referred to. If all of those parts were replaced, the CO and base idle should definitely be redone because what I think happens is over time as air leaks get introduced into the system or the ISV, TPS or plugs start to go out, people compensate by adjusting the idle instead of really fixing the problem. Once all of that is back to factory spec it can run worse until the MAF and the idle are reset as well.

Imo000

Yup that's where I was going.

Lance A

I appreciate it guys! I havent had a chance to do anything yet, and im going to have to borrow some tools, but ill keep u posted.

Mike-
Hot or cold it still idle hunts and requires gas to start.

soontobered84

So Lance, Have you or have you not replaced that O2 sensor?

Tech session at my house on Saturday.

Lance A

John-
I replaced it last sat but it made no difference. The exhaust bolts were a BITCH. However it definitely needed to be replaced anyway. What time is your tech session this sat? Ill bring the bathroom bid with me.

PorKen

If the idle control valve is original, then replace it. The motor wears out; cleaning doesn't help, unfortunately.

I've seen that they either don't work at all, work intermittently, or they have trouble opening (no cold start), or trouble closing (high idle).




A newly purchased '85-'86 will almost always need these original parts replaced as soon as you get it home.

Minimum to idle properly:
ICV
O2 sensor
Spark plugs
10 upper intake hoses
CO/idle speed adjustment (Blink'r)

And often needs:
TPS, harness
Long ICV hose to 'T'
Temp II sensor (coolant)
Rebuilt MAF, MAF o-rings

For general running:
Fuel filter
Fan clutch
Plug wires
Front crank seal
PKsn'r, timing belt
6 cam end seals ('85)
Distributor rotor, cap
Crank position sensor
Jump post cap + cover
Temp I sensor (airbox)
Water pump, new WP bolts
Thermostat, o-ring, rear seal
Cam/oil pump gears (if coating worn)
Cam timing check/adjustment (32V'r)
Flexplate release, PKlamp (auto)
Fuel pressure regulator return hose (bulk 7mm ID)
Air filter (throw away K&N, clean dirt from lower airbox, MAF/TB housing)

Mike Frye

Good list Ken,

I would add: check/confirm that TPS is working and being read all the way back to the LH. I've only been involved with a few of these, but they've all had loose connections at the plug, had the TPS full of oil and 2 of them had some kind of silicone holding the plug together and at this age, they all have brittle wiring that's cracking all over the place.

PorKen

True. True.

I'll add a few more too. I just did a big refresh on a worn '86.5 for a first timer, so it's fresh in my mind.