3vzkillingme

Hi YT, first-time poster, long-time lurker. I have an '89 Toyota Pickup with a 3VZ-E and it's driving me nuts. Once it warms up, the idle gets low (5-600 RPM) and it hunts very evenly. Doe not stall. I've read as many idle threads as I found and have done the following so far:

- replaced the throttle body with a junkyard unit. "New" one was blasted (is very clean and smooth on all surfaces, and blown out to make sure all air passages and coolant passage were clean. Also replaced idle-adjustment screw o-ring
- changed plugs for OE NGK, wireset for NGK, and adjusted ignition timing. No change
- adjusted the TPS. No change, but I did notice that the original TPS (I am not the original owner, truck has 240K at least) was blue-labeled P/N 89452-28030 and so was the replacement TPS that came with the throttle body. According to Toyota's parts system, that is incorrect and the right one is 89452-14050 (brown-label, which apparently only came on trucks built between 3/1989 and 7/1989. Mine is a 6/1989 build date). HOWEVER, the truck was running fine with the supposedly-incorrect TPS before this all started. When it's hunting, if I jumper TE1 and E1 I can't discern any change in the idle (I thought it was supposed to lower, and that this was a sign of improperly-adjusted or bad TPS)
- changed out the nasty green-brown coolant for Toyota Red. Bled properly. I read that water pumps going bad can cause idle issues and do not know if the pump is bad, but I do hear a squeaking noise from the pulleys. Not sure if belts or water pump or fan clutch. Timing belt was done at 200K according to the sticker on the cover, do not know if WP was also changed out
- changed the O2 sensor with a Denso. So rusty and dirty I couldn't tell if it was original; no change with the idle, but the strong gas smell I encountered disappeared
- somebody had plugged off the third vacuum line coming off the top of the TB (not one of the two for EGR); reattached that. No change
- found vacuum leak: P/S idle up vacuum line (only found one, switch on P/S pump only has one port. Not sure if this is correct because the vacuum diagram is no longer on the hood) was hanging loose; plugged it as I don't care about P/S idle-up, it leaks bad so doesn't work anyway. Idle raised as soon as I plugged it from 550 to 620 RPM, but still hunted. After adjusting warm idle with the screw on the throttle body again, restarted truck and same problem
- replaced the air intake hose connected to the TB due to crack at TB; no change
- replaced a kinked hose at the fuel pressure regulator with a new OE one (it was some parts-store garbage). No discernible change
- checked to see if the AFM vane was getting stuck as per a couple of threads; no such luck
- taped off the idle bypass hole in the throttle body as per a thread where a guy was having similar issues and his warm idle normalized after doing that. No change

I bought an ECT sensor, but haven't put that in yet. As I mentioned truck doesn't stall currently, and it runs fine, just has the loping idle that shakes the whole truck. If I use the warm idle-adjust screw to raise the idle it runs a lot smoother and shakes are reduced, but it does weird things: if Istab the throttle immediately after, it'll start raising the idle until it hits almost 1100 RPM. Then, if I restart the truck it may idle fine for a bit at 800, but if I drive off, it'll be back to hunting idle by the first time I stop. It's like the idle adjust screw changes the warm idle but restarting the truck throws all that out the window and the ECU tries to set the idle.

Any help would be greatly appreciated, I need this truck for work and I don't know when it'll get worse and have to be shelved. Thanks!

3vzkillingme

Welp, figures I set up the solution in my post and found it right after, lol. Somebody broke the other nipple off the idle-up switch; there were two vacuum lines to block off. Engine runs a dream now.

87-4runner

Nice catch... thank you for reporting your conclusion.