High idle

[Jrato14]

Hi all so my struggles continue but this forum has been instrumental and so far I have solved most problems. I have the 5.0gxi Volvo that I have poster about before. One engine was a new long block. When I start the engine in neutral it appears to run at max rpm’s even with the throttle disconnected. The tps was disconnected when I bought it as was the air control so I attached them which has not fixed the problem. Any help would be greatly appreciated

 

[Scott Danforth]

Is your throttle cable holding the throttle open?

 

[Jrato14]

Even when it is disconnected it does it

 

[Jrato14]

And it looks to be the same as the other engines

 

[dubs283]

Have you verified the throttle plate is wide open? If it is, something may be broken between the throttle arm and throttle plate shaft

If it is closed there's a vacuum leak somewhere. First thought is pvc line disconnected

 

[Scott Danforth]

If the throttle is closed and the motor still runs above idle. Something is broken.

Look at the IAC, plug in Rinda, see what is out of the ordinary. Check fuel pressure, see if you have a leaking injector or a wonky regulator

 

[Jrato14]

I don’t have Rinda. It is a brand new engine that only went through the break in period though. I am assuming the pcv line is what was meant right

 

[Jrato14]

When I say it is full throttle I mean full throttle the second it starts

 

[Scott Danforth]

I don’t have Rinda....... I am assuming the pcv line is what was meant right

Get Rinda

No, IAC. Idle Air Control

 

[ESGWheel]

Jrato
To help provide some background, with these 'modern' engines with fuel injection they use a verity of sensors (like the TPS you mentioned) and, to control the air flow for a proper idle, an IAC. Its sits on the side of the throttle body and is easy to replace. An VP branded one will cost hundreds but can get aftermarket (AM) for about 50. So, while it may not be the issue, without a Rinda diagnostic tool ($$$) you are into troubleshooting by ‘shot gunning’, i.e. replacing parts in hopes of finding the issue. This can also be costly but an AM IAC to troubleshoot is not a bad idea IMO.

Also be very cautious of a start where the engine immediately goes full throttle. This can damage your nice new long block due to lack of being fully lubricated.

 

[dubs283]

Yes, pcv line, sorry for typo

The engine cannot go full throttle without the throttle plate fully open. Verify how far the throttle plate is open first. Maybe something is bent or broken, this is for you to determine. Until then everything is just a guess

Doesn't take much air for the engine to exceed idle rpm by a wide margin. A seemingly small vacuum leak can allow a lot of air into the intake and with no load on the engine rpms can increase dramatically

If the tps is functioning properly the ecm will adjust injector pulse width accordingly. If the tps senses the throttle plate wide open the ecm will not signal the injectors to pulse. This is a clear flood mode designed to starve the engine of fuel and flood it with air.

Even if the iac were completely open 100% the engine would not rev beyond 1000 rpm without the throttle plate open under normal operation

 

[Jrato14]

Well once again, you all were correct. I swapped the IAC from the other engine it was rusty and old and fixed the problem. Now I have to order the correct. Once again you all are life/ money savers

 

[Jrato14]

So the saga continues it is definitely the IAC, but they are backordered from Volvo indefinitely. Is it possible that the engine is to relearn the sensor? What using aftermarket?

 

[Scott Danforth]

So the saga continues it is definitely the IAC, but they are backordered from Volvo indefinitely. Is it possible that the engine is to relearn the sensor? What using aftermarket?

It's a GM IAC. Check the SMP link in the electrical sticky and then go to your local NAPA

Mercruiser uses a Ford IAC