Another “surging idle” problem

[Daryl]

After new MAF, new IAC sensor, new plugs (.042) and wires, my surging idle problem is back. Hangs anywhere from 2000rpm to 1500rpm. Sometimes it drops down to the usual idle (950rpm) on its own. Other times I have to goose it, which of course causes the rpm’s to increase but after that it drops down.

The IAC sensor is clocked correctly and is set in place with a grommet and sealed tight with high temp silicone sealant.

The MAF is a new unit that came calibrated for 24lb injectors (I run Accel 24lb)

Plugs are the brand and # that are recommended by AFR for my 165 heads. And the wires are now 8mm with 90* boots where needed because one of the MSD 8.5’s got fried on the exhaust manifold.

Car also stalls due to no fault of mine. It has stalled in two different scenarios: 1.) being when I put it in reverse; and 2.) when I’m stopped (for example at a stop light) and the hanging idle finally drops down but drops too far and stalls the motor.

I feel like I did everything right with the installation of the new parts, so why has the hanging idle returned?

1,000 threads on this but wanted to lay everything I did out in case anything sends up a flag.

Thanks everyone!

 

[Daryl]

And as luck would have it, almost immediately after posting this thread, I lucked into a Google search regarding the same thing. That lead me to an IAC “motor” (which I didn’t know of!) and, after easily locating that the side of the TB, I ordered that AND its next neighbor, a new TPS. And judging by the look of both, I’d venture to say neither have ever been replaced. Are these both plug-and-play?

 

[ttocs]

be careful when removing the harness on the end of the TPS or any of the sensors really. The plastic clips are known to get brittle/break and it can cause issues once the motor is hot

 

[Daryl]

be careful when removing the harness on the end of the TPS or any of the sensors really. The plastic clips are known to get brittle/break and it can cause issues once the motor is hot

Good to know. Thx for the heads-up, Scott. Now in the holding pattern waiting for LMR to do their thing.

 

[96blak54]

To alleviate potential troubleshooting problems, install one and drive the car. If its good, install the other. Replaced components quality is subpar these days. Youll tract the problem quickly if one of the components doesnt cooperate.

 

[Daryl]

To alleviate potential troubleshooting problems, install one and drive the car. If its good, install the other. Replaced components quality is subpar these days. Youll tract the problem quickly if one of the components doesnt cooperate.

Also good to know, thx 96blak54 ! Think I’ll do the IAC motor first

 

[Terrorist 5.0]

I recommend not using silicone to seal anything. It can cause the O2 sensors to read funky and you COULD get issues, although I’ve never had any.

Then again, I only use a very small dab at the corners of gaskets, not a bunch sealing the intake.

I had a bit of an idle surge and it turned out my TPS voltage was off. This can change when adjusting the throttle plate. I would check the TPS voltage before anything, and try unplugging the IAC to see if the problem goes away.

 

[Daryl]

I recommend not using silicone to seal anything. It can cause the O2 sensors to read funky and you COULD get issues, although I’ve never had any.

Then again, I only use a very small dab at the corners of gaskets, not a bunch sealing the intake.

I had a bit of an idle surge and it turned out my TPS voltage was off. This can change when adjusting the throttle plate. I would check the TPS voltage before anything, and try unplugging the IAC to see if the problem goes away.

I’m unaware of TPS voltage. What should the voltage be, how do I adjust it (if necessary) and how do use the voltmeter to do it??

(remember: I’m admittedly an idgit with anything electrical). :-(

Did it again: Googled & found a YouTube on it. Maybe I should try that first before posting (roll eyes)

 

[07GtS197]

Setting the tps voltage is a myth. As long as the closed throttle value is around a volt and the wot value is around 5 volts and it increases/ decreases linearly you’re good. Looking for exactly 1v at idle won’t do anything for you. Test it and report back. It’s good to use an analog volt meter to check for voltage spikes when manipulating the throttle.

 

[ttocs]

as he said the computer reads the voltage dropped across the tps when it starts and sets that as the base idle reading. That is why the clips to keep it TIGHT are important because as it heats up it starts to have less contact which the computer reads as throttle input. Now it is a good idea to check it and ensure there are no dead spots where the meter stops reading but that should not cause surging IIRC.

 

[Daryl]

Thx 07 & ttocs. Saves me from chasing my tail on that one! Appreciate it and will definitely report back.

Now comes the challenge of getting that lower 8mm bolt out and back in…

 

[Terrorist 5.0]

TPS voltage is not a myth. Different brand sensors will read differently. Depending on how the throttle stop is adjusted, you can be in spec with one sensor and out of spec and surging with another. In general 1V at idle is good.

Now, they are not adjustable on SN95’s unless you drill out the mounting holes. The only way to do it properly is to adjust the throttle stop.

I only mention this because I had this exact scenario. I installed a new TPS sensor, and the car surged. Checked my TPS voltage, and it was over 1V. Adjusted the throttle and the surging stopped.

Ttocs, that is correct, a dead spot shouldn’t cause surging.

 

[07GtS197]

That’s a problem with the throttle blade position then not the tps itself. Most likely someone messed with the throttle blade due to some sort of idling issue. A base idle reset would probably have fixed the issue.

 

[Terrorist 5.0]

That’s a problem with the throttle blade position then not the tps itself. Most likely someone messed with the throttle blade due to some sort of idling issue. A base idle reset would probably have fixed the issue.

Not necessarily, as in my case, the voltage was too high. All I mean to say is different sensors will read differently, hence the need to adjust the blade sometimes.

 

[Daryl]

Once I figure out how to get the lower 8mm bolt off the IAC motor and then install the replacement, I’ll revisit a YouTube video about how to check amperage.

 

[ttocs]

I don't remember it being a big deal to get the iac out.

 

[Terrorist 5.0]

Once I figure out how to get the lower 8mm bolt off the IAC motor and then install the replacement, I’ll revisit a YouTube video about how to check amperage.

Take the distributor cap off and using a wobble socket and extension, remove the bolt.

 

[Daryl]

I don't remember it being a big deal to get the iac out.

My IAC motor has 2 spark plug wires blocking access

 

[ttocs]

are they mounted in a way that they can't be moved? I mean unplug them and move them out of the way for the time being?

 

[Daryl]

I’m thinking that’s what I will have to do