RPM once again

[werewolf]

on my 87 2.9v6 five speed. still have rpm's up & down. someone on here a while back said to plug all the vacuum lines. So i did i plugged off all the lines and it idle low rpm's 6 to 7 hundred a little ruff idle. and so one by one i hooked the vacuum lines up. the rpm's stayed low till i hooked the one to the map sensor and they went up to about 1400 and then to around 1100. you plug the vacuum line it drops. and the map sensor is brand new. So is the iac valve. So dose this mean i got a bad map sensor or what. the high idle is bugging the hick out of me. thanks for and help.

 

[RonD]

So if you unhook the MAP sensors vacuum line AT THE MAP sensor and plug it the RPMs are down at 650
So hose is good.

If you put the good hose on the MAP sensor and then suck on the end of the hose it holds a vacuum, so no leaks IN the MAP sensor

MAP sensor can't raise or lower idle, computer does via IAC valve if data from MAP sensor requires it.
So could be MAP or computer issue, or simply wiring between the 2.

IAC valve is a control, it just does what computer tells it to.
If you warm up the engine and then let it idle and unplug the wires on IAC Valve it will close all the way and the RPMs should drop down to 500 or engine may even stall, either is good it means no vacuum leaks.
If idle stays higher then there is still a leak.

Have you set the spark timing at 10-12deg BTDC with SPOUT disconnected?
MAP is the MAIN sensor for the computer, when it is disconnected from vacuum or electric computer runs in "limp" mode, factory air/fuel mix for RPM.

 

[werewolf]

map sensor

yes sir Mr. Ron the map sensor is brand new and also the IAC. And i did replace the the vacuum hose from intake to the map sensor, with a new hose. and after it warms up the RPM drop to around 800, and if you unplug the IAC the engine dies. And no sir. i have not done anything with the timing at all. but i did read a little in TRS library and did look and find this plug that needs to be unplugged. I mean the spout is what you call it. I found it but that's all have not played with timing at all do you think i should i do have a timing light some where. I work on heavy equipment, these old diesels i haven't used my timing light for ever. but i will if i need too. i'll find it.

 

[RonD]

"New" used to mean "tested and works"

"New" now means "you test it, we warranty it", so don't assume "new" part actually works, lol.

Yes, find the old timing light
And if you have a vacuum gauge it can tell you alot about a gas engine