BIZARRE Idle issue, any ideas?

[MrMazda92]

So, I finally managed to get the top section of the coolant fill pipe in place, cap and all.

I drove the car for 1 day, all was well. The next day I didn't drive until 10 at night, and the car would NOT drop below 2k at idle... even when I was in gear, it would sit at 2k.

Today, I checked all vacuum lines and checked my idle speed.

Vac. lines were good, as expected. When I jumped the ten and ground in the diag. box, the idle dropped to ~700... which is exactly where I set it, and it ran there until the other day. I pulled the paperclip back out, and the idle shot up to 2k again. I repeated the process to the exact same effect, 3 times.

Any suggestions?

Thanks!

[h3xt0r]

Aren't you supposed to pop the battery off aswell when you do that? Can't remember.

[Newfie_dan]

if the intake tube and all vac lines are good I would be looking at tps see if it got loose somehow and moved, you can try unplugging the iac but at 2k it sounds more like a tps adjustment. I would also check the resistance on the temp sensor see if its in spec, thats the 2 wire one not the 1 wire sensor, sometimes if the coolant level is low it can cause the idle to go high (car thinks its colder than it actually is).

[_-Night-Shade-_]

Did you get all the air out of the cooling system? If coolant isn't reaching the sensor it will have incorrect reading.

[MrMazda92]

It seemed like the TPS to me as well, I tried tweaking it without jumping the grounds, to see if it had any effect, and it had very little. I tightened it to fully closed, and the idle dropped to ~1,500, when it should stall at that point.

Minor update... No matter how long I warm the car up for, it will not drop below ~1,500.

However, if I drive with it in that condition... it drops down to normal after 20-30 minutes of typical driving. The problem is gone until the car sits overnight, and then returns.

I'm inclined to believe the coolant is the issue, as that was the most recent change made prior to the issue popping up.

I'm going to flush my radiator this week, and I'm honestly expecting to find a few small holes. Depending on the severity of the leaks, I'll plan from there.

[wytbishop]

When 10 and GRD are bridged in the diagnostic box essentially what's happening, is that the non-essential sensors are being bypassed. The sensors which are necessary to make the engine run, the PRC, VAF, TPS are all still live but the O2 sensors, coolant temp sensor...sensors which adjust the tune of the engine while it's running are not.

So when you set the idle with the jumper in, you're sort of setting it with only the mechanical functions in operation. Then, when you pull the jumper the ECU starts making adjustments bases on the readings from those adjusting sensors. If your idle is good with the the jumper, but bad as soon as you remove it, one of the "adjustment" sensors is giving a bad reading.

That's my take. For what it's worth.

[MrMazda92]

Thanks for the reply wyt, faulty O2 sensors should trip a CEL if I'm not mistaken? That would leave Coolant, Knock, and what else?

Also, diagnostic box aside, shouldn't closing the TPS all the way stall the engine? It does when the jumper is in, but when it's not jumped closing the TPS has VERY little effect. Jumping it with it closed stalls it, as well.