Cleaned Throttle Body, now high idle only in park/neutral

SkyVolvo · Post by **SkyVolvo** » 15 Feb 2011, 23:28

Hey folks -

So my '91 740 NA (178K) hadn't been running at peak efficiency lately. Some occasional low idling, some hesitation, until the other day it went crazy with a pretty strong rolling/surging idle and felt like it was going to stall when I came to a stop. The next day it ran okay, but I wasn't going to push it.

I'd done the plugs and wires recently, and my newest parts order came in, allowing me to do the cap and rotor and, today, service the throttle body. It was nice and gunky (not totally packed with sludge, but definitely in need of a deep clean), so I happily cleaned it all out, replaced the gasket, and reinstalled it.

When I started it up and drove it for a few miles, it was like a new creation - nice, fresh, springy throttle response. When I got back and parked it, though, the idle stood at about 1K and began slowly creeping up to 1300 or so, where it steadied out again. If the idle just stayed high, that would be one thing, but why would it slowly creep? Does that seem like a possible leak, like, say, at the new gasket? I did have some trouble getting the old one off the corners, but I worked at it and thought I'd gotten it good enough. Is there a way to check this without disassembling, re-cleaning, reinstalling, and hoping for the best? Is perfectly clean and perfectly smooth the only "good enough" for a gasketed surface?

Further info: I just went out to fiddle with it and see if I'd left a hose off or something silly. The directions I was reading had said to disconnect three vacuum hoses to the TB, but I had only remembered two, located on the top of the TB. I still only found two.

It really did not want to start (I've had some issues with it lately), so I switched the radio suppression relay and, thankfully, it started. Again, the idle started at just under 1K, and after a minute or so had made its way up to 1300. I found no disconnected hoses, but I did find codes. I had cleared my 2-3-2 code (Lambda Adjustment) after cleaning the throttle body, but it was back, along with a CEL and a new 1-1-3 (Fuel Injectors). What the heck? Did switching that relay out give me an injectors code? But if the relay was faulty, it wouldn't start at all, right?

Idea: would a bad o2 sensor cause the idle to rise as the sensor warmed up and began sending a signal? It really is just a slow, steady rise in idle - it's very stable along the way.

Oi. I really appreciate the responses from all of you, especially since the 740 forum seems to have much fewer dedicated contributors than other sections on the site.

SkyVolvo · Post by **SkyVolvo** » 16 Feb 2011, 07:46

I drove it to work this morning and noticed that while I was driving, everything ran normally - it idled fine at lights, etc. When I parked it at work, though, the idle quickly made its way back up.

SkyVolvo · Post by **SkyVolvo** » 16 Feb 2011, 22:15

So I'm going to go ahead and say, "I should clean the IAC tomorrow," and while I'm at it, "I should replace the flame trap with the kit I purchased." Any votes on whether this solves the problem?

Whitebrick · Post by **Whitebrick** » 16 Feb 2011, 23:06

I vote it will help a lot. I just cleaned my IAC, got a rewarding chunk of crusty soot out of there and sprayed with carb cleaner, and a lot of my surging went away. But not all, so I think there's still one or two things left to do. I don't have a flame trap, but you doing that too may get it all! Look forward to hearing the results.

SkyVolvo · Post by **SkyVolvo** » 17 Feb 2011, 20:23

Cleaned the IAC with no success; it's been recommended that I adjust my TPS, although I can't see how it would have moved, and it seems to click open and shut at the appropriate spot. I started trying to adjust the base idle, but once I loosened the lock nut, I couldn't see how to adjust the screw. Anyway, I would think it strange if it were the base idle - it never had a problem before, and even now it's not a steady problem, but one that increases as the engine warms up.

Whitebrick · Post by **Whitebrick** » 17 Feb 2011, 23:00

What about the flame trap?

SkyVolvo · Post by **SkyVolvo** » 21 Feb 2011, 20:48

Alright - I've been delayed by a fuel filter job gone wrong (couldn't get the blasted thing off, but did break the seal enough to leak gas). Once again, I found myself goofily explaining to my mechanic what I'd done, and what needed to be fixed.

Anyway, I was able to service the flame trap. The trap itself and the small vacuum hose coming off it were actually fairly clean, certainly able to pass air easily. The hose, however, going down to the oil trap looked like hell. It was probably original, and tore down the side when I removed it. "Ah-hah!" I thought, "This must be the vacuum leak..."

Unfortunately, it wasn't. I'm glad I replaced it, but my high idle remains. I'm seriously looking into the possibility of a new o2 sensor, given the rotten mileage it's getting and the 232 code. I'd like to find where the o2 sensor connects - my understanding is that I can unplug it and see if the problem changes when the car stops getting info from the sensor and resets to its automatic settings.

Schumi 1 · Post by **Schumi 1** » 18 Mar 2011, 13:41

Hello, did you ever figure out the cause of your problem?
I have a similiar problem , also code 2-3-2 and hesitation on acceleration, but more of a surging idle. I have done all you have as well and pretty much down to fuel delivery ( pump to the injectors) TPS and o2 sensor. I swapped out the ECU and 2-3-2 came back...

bullet79 · Post by **bullet79** » 07 Dec 2016, 03:50

Anybody solved this?

SkyVolvo · Post by **SkyVolvo** » 07 Dec 2016, 08:47

I'll be honest...all this time later I have no recollection of whether I ever solved this. The car is still in the family and still running fine though, for what it's worth.