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Replaced IACV, now it's worse

bigalpha

Moderator
Location
Tucson, AZ
I replaced my IACV with a new one and the idle is ridiculous now. It idles about 1000-1200RPM with the old IACV. I replaced with a junkyard unit and it idled at ~2500RPM. Replaced with new and now it's the highest it's ever been.

What's the deal?
 
did you clean any carbon deposit in the throttle body where the tapered part of the IAC seats?
 
Yes, I've pulled the TB and cleaned it and cleaned out the carbon deposits from inside the IACV seating area.

It's like the IACV isn't closing at all and it's just opening up allowing max air flow.
 
Lol.

Why'd you replace the original one? Why not put it back in?
 
Mainly as a diagnostic for my high idle. I replaced it with a junkyard unit and it idled much higher than it does now.

Thinking my original one has gotten slow or defective, I replaced with new to see if it made a difference.

Well it did - but for the worse. Much worse.
 
95 or 88--which has the high idle?

If its the 88, check the EGR system, especially the vacuum transducer valve.
 
It's the 88.

I'll test the transducer tomorrow. I already tested the UFO and it performed as it should.
 
Sorry that wasn't clear.

I used a screwdriver to pull out the peg and the engine bogged down and died. When I let the peg go, it snapped back shut and the engine started right back up.

Also tested the EGR solenoid (on the fender) and one end had vacuum and the other was absent of vacuum, just as the lunghd article says.

Why would a new IACV cause a really high idle while the original IACV only a slight high idle
 
No on needing to adjust the TPS. That's all mechanical. I'd just reset it on the off chance, the computer needs to relearn the new IAC valve. Takes 5 minutes and it's free.
 
Alright, I'll give it a shot and see if it helps.

I was joking about the TPS and injectors - I was mainly making fun of that other thread where the guy won't adjust his TPS.
 
So I couldn't get the connector plugged into the new IACV. The connector plugs into the original IACV and a junkyard spare IACV easily. Must be a defect in the housing. I got it from Autozone (part # AC301)

I'm going to get a new one tomorrow and return this one. Also, I noticed the metal collar was slightly different on the new models - don't know if this was a design change or what.

5163337420_01bcc02452_z.jpg
 
The Renix ECU has no memory. The ECU maintains power to the B Latch relay for 3-5 seconds after shutdown so the ECU can "center" the IAC for the next start.

Unhooking the battery on the Renix has zero effect on the ECU.

bigalpha, let us know what you find.

PS--I have the full EGR/transducer test procedure from the FSM copied, let me know if you need it and I will post it up.
 
I guess my last reply didn't make it.

Looks like I reset my radio presets for nothing :p

No place in my town has an IACV in stock except for the one I picked up that won't work. For now, I guess I'll stick to my original.

If you have a full testing procedure for the EGR system, that'd be great. I tested the components according to the lunghd article and my system tested out OK.
 
From the FSM 90:



Warm the engine to normal operating temperature.


Operate engine at idle speed.


Check vacuum at solenoid vacuum source.


Disconnect the hose and attach a vacuum gauge to it.


Vacuum should be at 15 inches.


If vacuum is low, check the line for kinks, twists, or a loose connection at vacuum connector on intake manifold.


If vacuum is ok, remove gauge, reconnect the line and proceed to next step.


Check vacuum at solenoid output port.


Disconnect the line and attach a vacuum gauge to output port. Vacuum reading should be 0 at this side of solenoid.


If vacuum reading is 0, leave the gauge connected and proceed to the next step. However, if vacuum is present check solenoid/ECU operation with the DRB-ii tester.


Disconnect electrical connector at solenoid and note vacuum at output port. Vacuum should now be present at output port.


If vacuum is present, proceed to EGR valve test. However, if vacuum is not present, replace the solenoid. Test the EGR valve as follows:


Leave solenoid electrical connector disconnected. Note the engines idle speed.


The engine should idle roughly or stall. If this occurs the valve is ok. If the idle does not change, proceed to next step.


Disconnect hose from the EGR valve and connect a hand vacuum pump to EGR nipple.


Apply a minimum of 12" of vacuum to the valve and note engine idle. If engine now idles rough inspect the vacuum line between the EGR valve and the solenoid.


If the idle did not change, remove the EGR valve and inspect the valve and the exhaust passage in the manifold for blockage, repair as necessary. If no blockage is present replace the EGR valve.


Vacuum Transducer Testing as follows:


Disconnect the transducer vacuum lines and back pressure line. Remove transducer.


Plug transducer output port. Apply 1-2 PSI air pressure to transducer back pressure port. Air pressure can be supplied with a hand operated air pump or compressed air (regulated to correct pressure). Apply a minimum of 12” of vacuum to the input port.


Replace transducer if it will not hold vacuum.
 
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