jonpanic

Hey all,

I've had this 1987 4runner for a few months, and I'm having some problems getting it to run well. At first it would consistently miss on the first cylinder. I replaced several cracked and worn vacuum lines and routed them properly, along with replacing a cracked PCV hose and a cracked valve cover breather hose. I also replaced the cap and rotor, plugs and wires (NGK), coil (which was out of spec), it now seems to run on all 4 cylinders. When I set the timing to the factory recommended 5 degrees, it has an irregular pop coming from the tail pipe and has really poor acceleration. Advancing the timing seems to help a little with the power, but there's still something wrong. I'm going to check the ECU for codes, but it's a automatic that's been converted to a manual, so I'm not sure what kind of codes I'll get. Another thing I noticed is the tach often gets stuck around 2K RPMs and stays there until I restart the truck.

First thing I want to check is my timing chain for slack, but I also think there might be a problem with my TPS, Idle control, or igniter. When I start the truck it doesn't increase the idle and drop down after it's warm. Sometimes when I start it, it stumbles around 500rpm and after a few quick revs it stabilizes to around 750. Any idea what causes this? I've heard that a faulty igniter can cause tach issues, but the spark seems fine (I'm an inexperienced mechanic so I might be wrong about that). I've also heard that the TPS can cause all kinds of problems if it isn't working properly.

Just wanted to get your thoughts and document me chasing this problem down. If you have any suggestions of what to look at first, please let me know.

Thanks!

Edit: Just went out and checked the truck for codes and I got a code 11 which reads:

--A/C SWITCH/CIRCUIT
--A/C AMPLIFIER
--TPS/CIRCUIT
--NEUTRAL START SWITCH/CIRCUIT
--ECU

The AC doesn't work right now, it's been upgraded but I haven't attempted to charge it. The neutral start switch was also removed when it was converted into a manual, so that could also throw that code. I guess it makes the most sense to start with the TPS? I also noticed when I put the key in that the tach jumped up to it's sticking point at right under 2K.

Paul22RE

Have you cleaned the Throttle Body? Also check for any cracks/leaks on the intake hose leading to the TB. Also, check for any play on the TB shaft. Most thorough way to clean the TB is to remove it & use a new gasket. Do not get TB cleaner on the TPS, remove that before cleaning and then make sure it is within specs and adjusted properly.

Here is how to test/adjust the TPS: http://www.4crawler.com/4x4/CheapTricks/TPS/index.shtml

jonpanic

I haven't yet, but cleaning and inspection of the throttle body, intake hoses, and TPS seem to be the next step. Thanks for the link!

jonpanic

When I jump the terminals to set timing there is no change in idle speed, which points directly to a faulty TPS according to that article. I went ahead and placed an order for a new one and a throttle body gasket. I'm going to give everything a thorough cleaning, install and adjust the new one and see how it goes.

jonpanic

Today I removed the throttle body and cleaned it thoroughly. I had the most luck using a small nylon brush that fits into my drill and lots of throttle body cleaner. After replacing and adjusting the TPS and reinstalling all the hoses, it ran much better. I checked the diagnostics and have no engine error codes. I'm still having a popping from my exhaust, which I think is being caused by a pretty big exhaust leak. I'll let you know if I have any more problems after I address the leak.

Paul22RE

Glad to hear it is running much better!

snippits

Did you buy a Denso TPS or another brand?

87-4runner

Popping might be a value not seating properly...

jonpanic

Would a compression test help me determine this?

jonpanic

I grabbed one local, it's made by Standard Motor Products. It's Chinese, but I checked to make sure it met all the specs before installation, and it carries a lifetime warranty. I'll let you know if I have any problems with it down the road.

millball

Valve lash adjustment first., If not already recently done.

jonpanic

Seems like my idle control might be stuck open. I double checked my TPS adjustment, went through all the vacuum lines, and my idle is still high. I may try bypassing it, setting the timing and see if this helps with my occasional misfire. I still have to do a valve lash adjustment as well. Thanks everybody for your help.

ev13wt

Open hood, engine off, turn throttle plate by hand and let it snap shut. It should have a damper on it making it close slowly (much slower than the force of the spring). This stops the popping / backfiring if installed and properly adjusted.

Does it now drop idle when you jumper the test connector? Else, buy a tps from 22reperformance - not that ebay thing. It's probably the cause of the issue.
Heck, even using aftermarket cap and rotor will screw up everything to the point you start troubleshooting.

jonpanic

I don't seem to have the damper, it snaps closed with the full force of the spring. Does anybody know what this part looks like or it's part number I can reference? I swapped out the TPS for a real Denso unit, adjusted it and still have the popping and a high idle. Would I need this damper you mentioned to properly set the TPS? I might need to clean or replace the IACV as well. When I squeeze the large 5/8" line that comes off the bottom of the throttle body, it causes the idle to drop.

I also adjusted the valves and set them a tad loose, just to see if one was stuck open. There's definitely more valve chatter but this didn't help with the misfire.

jonpanic

Also, my tach has still been acting strange, sticking right around 2K rpm. Should I consider replacing the ICM?

RASALIBRE

The “dampener” you are referring to is called the dashpot.
Google image search: 22re dashpot.
Google search: LCE PERFORMANCE throttle position tech and adjustment procedure. Brings up a 4 page pdf, step number 8 deals with the dashpot.
I’d make sure your idle air control valve (IACV)/auxiliary air valve is working properly. They’re known to be finicky in their old age.
They can be taken apart cleaned and maintained, but there is a coil involved that can be fried. They can be swapped for an 89 or newer upper intake manifold and throttle body. The 89 and newer throttle body has the IACV integrated in.
22re-early-late-intake-swap
Or you can replace your current one with a Nissan version that doesn’t have coolant passages. You’ll have to do some searching of my old posts for that.

What ever came of your exhaust leak suspicions? An exhaust leak can cause issues very similar to what you describe.

RASALIBRE

There’s 5 ways I know of dealing with a bad IACV.
1. Remove it, clean it, test it, if all good, reinstall it.
2. Delete it, deal with overly rich, bad cold starts.
3. Find a good used one.
4. Update throttle body and upper intake manifold to an 1989 or newer. See link above.
5. Use a Nissan part number 22660-01U10, you’ll need to fabricate a bracket.

jonpanic

Very cool. I came across the dashpot info in the factory service manual, but I'm not sure if the dashpot is going to fix my problem. It seems more like an emissions device than something that should effect performance?

I had the exhaust leaks welded up, but I still am having some issues with the popping and misfire. If I get a chance I'll record a video of the tailpipe to share.

I like the idea of replacing the IACV with the more available Nissan part. I'm going to do some googling.

jonpanic

A few updates. While I was readjusting the TPS I came across a big crack in the rubber fitting that connects the throttle body tube to the AFM. I had no luck finding anything local, so I taped up the current one for the time being. This dropped my idle WAY down (almost stalls now with the idle screw all the way in). Still getting the pop and miss, but I feel like I'm getting closer. I also checked the readings on my AFM and everything was to spec. I might try replacing the ignition module to see if this fixes my strange tach and the miss. Thoughts?

RASALIBRE

The ignition module (called the Ignitor) is pricey. You have a fsm? I’d go through all the checks in the IG section before I dropped money on a new ignitor.