IAC question

[fiatslug87]

1990 4.0L 5 speed. My idle will increase as the engine warms up. When I push on the IAC the idle starts dropping, there is movement in the valve at the front where the electrical connector enters the valve body, not at the throttle body. I will be replacing it, my question is should I go with MOPAR (>$100) or aftermarket (<$40)?

[Dzimm]

I've never had issues with mid-priced aftermarket sensors I've gotten from autozone.  I have always avoided the cheapest aftermarket options.  Saying that, there are a lot of people who insist on Mopar sensors and I would use them if I could afford to use them every time. 

 

You will get tons of opinions both ways but to me it really boils down to how much you can afford/want to spend at the time.  Mopar is best but the aftermarket options do work.  

[PCO6]

I'm with Dzimm on this.   I usually go to NAPA for this kind of thing and I've never had any issues.   I'm not saying their parts match MOPAR but I do know that they've never let me down. 

[DirtyComanche]

The SMP one is probably okay.  SMP151 I think is the P/N, but that might be for the HO one... Just make sure there isn't a T on the end of the P/N.

 

I've honestly never bought a new one. Normally the junkyard is full of new ones from people trying to fix idle issues that weren't the IAC.

 

Are you sure the o-ring on it is good?  And the plunger is clean along with the little passage for it?

[cruiser54]

I wouldn't be afraid of a used IAC. 

[fiatslug87]

8 hours ago, DirtyComanche said:

Are you sure the o-ring on it is good?  And the plunger is clean along with the little passage for it?

Yup, all is clean and the o-ring looked good.

[metrictonner]

I've found that the stuff that gums up the throttle body also gums up the IAC pintle shaft and pintle keyway inside the IAC.  I can't imagine any way of cleaning the pintle shaft and keyway without screwing up the grease on the stepper motor threads.  An expensive IAC is just as sensitive to being gummed up as a cheap one although I've found that an expensive one will PROBABLY run better at first.  A start up that doesn't go right to idle but bounces to 2000 or so RPM most likely indicates an IAC that is poorly made or starting to stick.  That's right, a 2000 RPM bounce is NOT normal, take this from someone who owned his MJ since it came off the assembly line.

 

All this talk about cleaning the throttle body would only fix an IAC problem where the pintle is stuck in the trottle body when it is fully extended which means there is no bypass taking place which means that the thing won't idle...or even start.  A high idle probably means the pintle is stuck open (retracted) and won't extend to decrease the bypass, decreasing the idle.

 

Being able to decrease idle by pushing on the back of the IAC either means the mount is loose (not screwed in tightly) or the o-ring is screwed up (pinched flat spot or tear) because either way you are advancing the pintle head in the throttle body, decreasing bypass, lowering idle or blocking an air leak around the o-ring.  It could also mean, although I have never seen this, that the stepper motor is busted loose from the mounting inside the IAC and is sliding back and forth in the IAC, although I would think the ECU would try to make up for this by just juicing the stepper motor until the idle is correct like it normally does. 

 

I seem to recall, a long time ago, that there was a big thing in Chrysler dealerships that attempted to fix injector leaking by replacing the factory Siemens Deka's (the AMC Jeep Bendix Deka's didn't have this problem) with Dodge Neon's. The dealers didn't think much of the problem and only did something if the customer complained.  Having an early factory MJ that came with Bendix Deka's I never got into this.  No maintenance chit was ever wrote up for this so I don't know if the injectors were leaking internally or externally.  An internal leak would put a puddle of fuel in the intake manifold and cause the idle to pop on start-up, I suppose, but the 2000 rpm pop is so consistent,  hot, cold, first, last, I doubt it is due to leaking.  Maybe there is an ex-chrysler-jeep mechanic out there who can fill us in.  A couple of years ago I actually bought a complete set of Siemens Deka's from a local dealer who had these things laying around due to the customer fix (20 years ago), at a sizeable discount, he just wanted to get rid of them.  They work fine for me and a lot better than the crap advised to use on this board, including the Dodge Neons.  Renix was designed around Siemens injectors.  AMC Jeep got Bendix to make them stateside and when Bendix got out of autoparts Siemens took over the Bendix injector factory until Chrysler stuck their own injectors in the 4.0. 

 

 

 

[fiatslug87]

The mount was not loose, there was movement at the front where the electrical portion enters the valve body, no movement at the TB.

 

Well, I went with the NAPA IAC, in stock and 10% of when reserved online. My idle now stays at ~800 RPM (cluster tach) and I haven't gotten the occasional high idle at startup.

[coolwind57]

1 hour ago, fiatslug87 said:

The mount was not loose, there was movement at the front where the electrical portion enters the valve body, no movement at the TB.

 

Well, I went with the NAPA IAC, in stock and 10% of when reserved online. My idle now stays at ~800 RPM (cluster tach) and I haven't gotten the occasional high idle at startup.

 

Napa runs about $60 in my neck of the woods.  Ebay often sells for 10-15 bucks.  I think a MOPAR unit is on ebay for like $145.  Crazy differences.  It's all a toss up on how one makes a decision on buying IACs it seems.