91 Toyota Hilux
2.4L
Manual Trans
4x4

I've done a lot of reading on here and couldn't find anyone who had the same idle issue that i was having. Which made it hard for me to diagnose, along with the fact i'm very much an amateur. The surging has been going on for about a month. Coincidentally ever since the truck and i decided to get friendly with a snowpile(knew i shoulda stayed in bed that day).

My idle problem was all the time when it was in neutral. Brakes applied or not. I seen this was a common problem if the brakes were applied only and a lot of others found success in the idle screw itself. Applying tape and tightening it back down. This was the last thing i wanted to try. Was certain it wasn't that.

I changed the Coolant temp sensor after a bit of research. No Luck
I checked all the vacuum lines. Found one very small thin line under the throttle body that had a hole. No Luck
I checked the cooling system for air bubbles. No Luck there either.

Then moved on to the TPS. (didn't ohm it, and it should've been the first time). removed it checked it out looked fine. reinstalled. Didn't seem to make a difference, checked out a few other things. And after that, i had a whole new set of issues. The truck surged all the time. In gear, or in nuteral. I lost my brakes almost completely, and the truck seemed to decide to apply throttle all on its own. Parked it for the night and decided to look more into it the next day. Looked around on here some more.

Next day. Bought another TPS for 100 bucks. Looked around at some other lines and Ohm-ed the TPS, it read within the limits but on the lower end. Didn't figure it was that. Then started to suspect the Air Flow Meter, Ohm-ed that and it was Dead. No resistance anywhere. We then re tested the TPS and it also came out dead. We stole another AFM from a friends V6 who was close by to test. Made no difference, but also parts weren't compatable. Tried holding the flapper. It made a world of difference, the truck idled like it did back on the day i bought it. There wasn't any autoparts stores near me who had one in stock nor was i really willing to pay 300.(on a bit of a budget atm.) and i had a high suspicion my dad might have had one lying around in the pole barn. i just had to make it there. Started her up, she still surges in neutral but brakes were back and i had correct throttle response. The truck was just jerky when i got off or on the throttle.

So i had a bad Throttle Position Sensor AND a bad Air Flow Meter, which i will change tomorrow. 2 parts at the same time. what are the odds....
Anyway i hope this is helpful to somebody! i know its been driving me nuts and i'm just really glad to have figured it out!

 

You didn't mention if you have checked the ecu for codes. That's the first thing to do. Also if you keep the bad TPS unplugged it will usually run better till you get it replaced. Also you should be able to source an AFM from a wrecking yard or craigslist or the yototech classifieds. Where do you live? I have an extra AFM or 2 laying around. I'm sure others on here do as well. Good luck

 

Unfortunately the truck showed no codes. Which also made it frustrating. And the truck ran the same with the old tps unplugged. I live in northern Michigan. Going to search today and if I can't find one I'll def check out the classifieds or letcha know. Thanks!!