1sennafan

My '89 22re is running good but just started idling rough maybe 1/3 of the time. No problems when its cold however after up to temp I’ll stop at a light and sometimes its fine and other times the idle will drop down to 500 or 600 RPMs and vacuum drops to 17” or 18” and of course it runs rough that low. I have found a vacuum leak is a vacuum leak all the time and is usually pretty easy to find and fix, that’s why I installed a vacuum gauge but this is different. It’s the “sometimes” part that is confusing me. There are no codes in the ECU, its running good at speed, idle is set at about 800 RPMs, and normally vacuum at idle is 21” and its smooth.
For some reason I’m thinking O2 sensor, but that should leave a code in ECU shouldn’t it? And shouldn’t an O2 sensor last more than a year or two?
Any one had this problem before?
I have FSM but just thought if someone had been down this road before it might save me some time instead of testing EVERYTHING under the sun to find the problem.
Thanks

nothingbetter

kinda sounds to me like you need new plugs. Of course it could be a bunch of other things too. Try something for me. Drive like a bat outta hell for 5-10 min then let it idle, does it smooth out? Driving hard heats up your plugs and will clean off some of the crap (if there is any) allowing for a better spark. If that makes it run smooth for alittle while, change your plugs.

1sennafan

Yeah I can’t find any rhyme or reason as to when it acts up.
I ran it home from work yesterday at 70 and 75 for almost an hour and as soon as I got off the highway (first light) it started idling rough, then the next three lights nothing, then at the last light again rough and then at home all normal. I always pull a plug or two to see how they look any time I have an issue. These only have maybe 2000 miles on them, and they have the normal light gray deposits, as they should.

Reading the plugs is the only real way I know to tell if the motor is tuned and running correctly on a pre-OBDII vehicle.
I’m also amazed with what a vacuum gage can tell you about what’s going on while its running if you know what to look for. I have put one in all but one of my vehicles and depend on it with this truck.

1sennafan

Well I changed the plugs for the fun of it and they are not the problem. However #4 was almost seized in, and it had heat glazing on it.
Filled it up and my mileage went from 18.2 to 19.4.
Im still thinking O2 sensor leaning it out. That’s were Ill start with the testing.

Kiroshu

On these old trucks the O2 sensor does not play that big of a roll in fuel trim. Most all of the fuel trim is determined prior to burn time. The AFM(Air flow meter) and TPS(throttle postion sensor).... Coolant Temperature sensor umong a few others determine 90% of the yotas air fuel ratio.

On OBDI vehicles if there is a vacuum leak the engine speed will be lower at idle.

Where as an OBDII vehciles idle would be higher as the OBDII computer compensates for the vacuum leak.

Idle speed and igntion timing incorrect?

Sticky throttle plate and idle speed set too low?

Dirty throttle body vacuum passages?

Leaky Throttle body and intake manifold Gaskets?

Improperly gapped spark plugs?

Leaky intake hose(between throttle plate and AFM)?

Dirt Driver

Failing O2 sensors don't always trip a CEL or code. I don't know about with these trucks specifically, but O2 feedback is often ignored during idle(and full throttle). It is used mostly during part-throttle cruise to keep the AFR around stoich for better fuel economy and emissions.

When the 200,000 mi sensor in my truck was failing, it caused slight low-throttle bucking and only tripped a CEL occasionally until I replaced it. The idle and economy was unaffected. My truck still has an intermittently low idle problem that predates the sensor failure that I still haven't isolated. It has to do with the vacuum system, though, because blipping the A/C on and off will make the idle come up to normal in most cases. Other times it will just dip low when pulling up to a stop after miles at highway speed.

ChefYota4x4

iTrader: (5)

How many miles on her, OP?

I've had ONE FPRegulator cause an 'off and on' fluctuation at idle....

I've also had 2 TPS cause me issues with rough idle('off and on' as well). The more common problem I had with the TPS was a 'surging'... it would bog like a 25yr old dog, ...then out of nowhere, 2800rpm or so, BAT OUT OF HELL! Into second gear, lil bit of the same, but then not many issues in 3rd or 4th, as the load was less, I suppose?

Vacuum leaks CAN, as well, cause issues with our OBD1 Oldies(as mentioned)

The most common 'when it felt like it' issues I've had with 'missing at idle' have seemed to, most often, come from 'mechanical' issues, namely, in my case, 'top end drama'. lol. My CAM was bad due to terrible machining on the first build.... Replaced the CAM without pulling the head.... It improved.... Eventually, replaced the adjustment screws.... Still remained and even got worse.... Then finally, it got so ANNOYING and concerning as to future trips(breaking down in the middle of nowhere)... I tore it down and found TERRIBLY loose valves and that he'd only ground the valves and never replaced the guides(only the seals)... I only mention this to keep your mind open to anything. By the way... mine had NO issues when cold, only giving me gremlin-drama when at initial closed loop and onward..... FWIW.

Check the vacuum readings all up in there, and run a few vacuum 'PUMP' tests, as well.

ChefYota4x4

iTrader: (5)

Good points!

BTW, .... you anywhere near Pearblossom/Littlerock/Punchbowl/Fort Tehon rd./Valyermo/Big Rock Creek? MAN has that gone to hell since I first started going there 28 years ago..... Still, I like to hit up the back side of the Angeles as often as I can..... You wheel up there? Thought maybe I'd look ya up next time I head up there. LOTS of guys in L.A. that I know whom would love to adventure around up in the Back side of the Angeles, too.... Just seeing wuzup, ya know? lol

Dirt Driver

I'm on the opposite (northwest) end of the A.V. from Littlerock, actually. The I-5 is a shorter drive for me. I'm in a good place for wheeling, but I only have a stock 2wd truck. My offroading is limited to two wheels until I can get a 4x4.

1sennafan

OK today I got codes in ECU.
#22 Open or short circuit in water temp sensor signal.
#43 No STA signal to ECU until engine speed reaches 800 RPMs with vehicle not moving.
So onward we go

Mileage is around 340 or 350 thousand. Odometer is off due to tire size and I replaced it with one that has all the gauges out of a SR5 not to long after I got it.

JoeT

Subscribing... I have had similar idle issues with my 86 runner, although lately it seems to have "cured" itself.

ChefYota4x4

iTrader: (5)

Ahhh, ... right on. Nice area, man.... When you DO get the 4x4..... lemme know, k? lol. Nice to meet ya

I love how the FSM words things in a way that is NOT how we 'yotatechers' speak, lol.... Anyway, IF the 'Water Temp Sensor' they're speaking of is the Coolant Temp Sensor(right next to the Cold Start Injector Time Switch in the front of the intake, under the throttle body, ....then IT CAN SURELY cause issues with rough idle and more(bad mileage, etc.)..... Is it possible that you changed out the coolant or something and developed a big air pocket or something?

First, test the Sensor itself(if it's indeed talking about the CTS, not the Temp sending unit for the gauge).... It's a fairly easy test using a multi-meter. Then, if that checks out, try burping the system for the heck of it.... It's NOT uncommon, especially with that many miles, for the cooling system to develop TINY leaks that suck in air or worse... ya know?

Far as the STA test at the ECU..... I REMEMBER doing this and having wonky readings.... I realized, shortly after, I was doing it improperly...(NOT EVEN saying you are, OP.... just saying to re-read it and make sure you're hitting the key but not quite starting it, etc., ...or whatever it says that I misread a couple years ago)...... STA issues are usually followed by 'NO START'.........at all.

ECU testing is interesting.... and really told me nothing, as my issue was mechanical. Obviously you don't feel your issue might be, and you may be right.... But even the ''brk'' testing on the ECU.... know what it's for? >> Fuel Cut System.... It actually cuts the fuel to the injectors momentarily when you hit the brakes at an RPM over 1000.... When My idle kept creeping higher and higher at one point.... My idle would bounce, over and over, while my foot was on the brake and idling over 1000rpm.... Sorry, not rambling, just saying.... DON'T read too much into your 'results' at the ECU until you test the components themselves, ya know? You could have bad wiring to the CTS..... but I've never seen that but once in 1000's of threads I've read and commented on.

ChefYota4x4

iTrader: (5)

PS> Best wishes on the hunt, man! ..... Been RIGHT WHERE YOU ARE, ...... for months...... and months..... and over a year, eventually! lol. Your issues sound much more intermittent.... So hopefully you'll snag that gremlin and wrap it up soon!

4Crawler

iTrader: (3)

Might check the TPS and dashpot to see if the throttle IDLe contact is not fully closing:
- http://www.4crawler.com/4x4/CheapTricks/TPS/index.shtml
- http://www.4crawler.com/4x4/CheapTri....shtml#Dashpot

Could be the IDLe setting is right on the hairy edge and sometimes the ECU sees closed throttle and other times not. The difference is with the closed IDLe contact, ECU does the smooth idle, without that contact closed, it "runs really slow". There is a difference between those two modes. I had that issue when my dashpot was set a little too far in and would sometimes hold the throttle very slightly open and it would idle rough. If I tapped the throttle a time or two, it would finally close and smooth out the idle.

1sennafan

The Coolant Temp Sensor tests OK.
Actually I did replace the coolant just days before all this started, I didn’t even think about an air bubble in the system.
Lets go burp the sucker!
My idle will still bounce over and over, while idling over 1000rpm after a year and a half?
I fixed that issue just enough to get it inspected last year.
No STA signal to ECU? Is this just voltage from the starter sent to the ECU? Nothing special just a wire from the starter to the ECU?
The FSM doesn’t tell me much or I’m looking in the wrong place.

4Crawler

iTrader: (3)

That one can happen if you ever bump started or hot wired the starter to get it running. Probably other things can cause it including an intermittent connection between the ECU and the ignition switch (or wherever that signal comes from) - check the FSM wiring diagram to trace that circuit.

ChefYota4x4

iTrader: (5)

Great post, as usual
All I noticed when testing that at the ECU was that it was VERY brief in it's showing of a signal.... It only shows when you engage the STArter relay, between "ON" and "STA" on the ignition switch.... (IIRC... can't be sure, so don't quote me... and 4crawler, above and below here, would know best! lol).... I highly doubt it would cause the issue you're explaining, but again I can't be sure. I believe it's the signal of "completed circuit between IGNition switch and STArter... and again, as I said, Roger would know better, lol.

Never threw a code when bumping mine... but a buddy of mine did, after bumping his 85 4WD EFI PU..... he reset it the codes and it never returned.

Just in case I missed it......... Have you reset the codes? I mean, you already have them written down.... I would DEFINITELY reset the ECU by removing the 15A EFI fuse for 15 minutes and then start over. See if either of those codes reappear???

Something I just remembered, reading Roger's posts....... I DID notice a huge difference after properly adjusting my TPS per his tutorial at 'cheaptricks', AFTER setting the dash pot properly BEFORE the final adjustment of the TPS. Mine was a lil sticky, not too bad, so also as instructed by 4crawler/Roger, I did a lil lubrication of the dashpot piston using 'silicone lube'. When I adjusted the throttle stop screw/dashpot, I realized how my TPS was COMPLETELY off from where the FSM calls it to be on resistance readings/with different feelers, etc.

I also remembered that I searched for a particular gremlin forEVER........... it ended up being a REALLY wonky throttle body pivot shaft.... It had quite a bit of play in it and would get caught up. I believe my replacement throttle body is having issues as well, and I need to further investigate.>>>>>>(I am experiencing an occasional 1000RPM idle rise at lights on occasion..... Out of nowhere and seemingly random.... Could very well be related to my AFM ambient temp reading, as it seems to do it more when it's cold outside... But I'm not sure that's even possible.) << Just mentioning it because we ALL have to fish at times for answers.... Thank goodness for Roger and guys like him who've taken the time to make great write ups and PROVIDE GREAT PRODUCTS!

1sennafan

I did erase the codes. However it threw them again but this time it was just a minute or two after starting it up. It never had a chance to warm up. The Coolant Temp Sensor tests OK but now I’m wondering if its connection may be the intermittent part of my problem

I’m a little lost on the No STA signal to ECU. If its only a brief signal when turning the key why would it be getting it while in the run position or after 800 RPMs?

FNV

These two links are the exact problems I'm experiencing. Thanks so much, from someone who's never used a multimeter, etc.

-Sage

1sennafan

OK Problem Found and Fixed!
Temp sensor was fine it ended up being the conector was dry rotted along with the wires.
I put a couple of new ends on the wires hooked them up to the sensor and Wala! She works like before!