HIGH RPM WHILE SHIFTING

Boostedpimp said:

Following because I have a hanging idle only while moving as well.. with similar build.

Ported TFS heads
TFS stage 1 cam
Holly Systemax 2
70mm TB

Waiting on ect sensor to arrive to hopefully cure cold start issue then I'll be dealing with this so looking forward to any updates you may have going forward

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Well there are a lot of us dealing with the same issue. I’m stumped and reaching a conclusion that the computer is unable to control the idle or the IAC ports are too big and let pass too much airflow. This problem is not that noticeable on absolutely stock version but once we increase the volume and air fuel parameters it is more noticeable and annoying.

For now I went back to airflow restricting plate and definitely works nice, just a hint of hanging rpm. I will make more plates with a slightly smaller hole size until I hit the sweet size. On the side I expect to continue welcoming more ideas and suggestions and working on this particular issue.

Good luck to you

jrichker said:

@PonyGTrider

What is the minimum mechanically adjusted RPM you can get with the IAC & SPOUT disconnected?

The 65 MM throttle body passes more air at idle than the stock 60 MM throttle body; that is an unavoidable consequence,

Some throttle bodies have a hole with a rubber plug in them. The rubber plug may have a hole in it which provides additional air flow that does not depend on the mechanical adjustment of the throttle body stop screw,

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Thank you for your reply
I’ll start by saying that I bought the TB and was used. It had a really big venting hole on the throttle blade and it was almost impossible to have a decent idle, for this I corrected it with a pop rivet and removed the tiny ball that expands the river leaving an oriffice of a out 1/8”.

I did followed a set of instructions on how to set the throttle sop by using a 0.010” feeler gauge and that’s the way I have been running it for a while. Well yesterday when I installed the IAC With the gaskets in between the body and the solenoid (Bo open airflow) I had to turn the throttle stop a bit more than one turn in order to get 600-650 rpm. I sort of expected that because the new IAC set up would let pass that extra flow from a normal open flow IAC.

On the TB I can go slightly under 500 rpm. With IAC and spout off

What do you thing? And thanks again

7991LXnSHO said:

It seems your theory is leading you the wrong direction. Limiting the IAC’s flow limits the computer’s ability to use it. Something is not set within parameters or is sensing wrong.
To fix idle problems, Ford made a plate for the the trucks to allow adjustment of more air at idle without having the throttle plate open so far. Others cut a bit out of the IAC gasket or drilled holes in the IAC divider wall to do the same thing on the cheap,
If you follow the Surging Idle Checklist and base idle reset procedure here, your vehicle should at least run better if not correctly.

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Thanks for your reply,
You could be right just let me tell you that I have that plate you are talking about. At this point I have the two bypass set screws closed.

I don’t want to sound negative but a have ran almost if not all the surging checklist without success. That only thing that worked the best for me at this point is the home made restriction plate with a tiny hole, just need to fine tune that hole size to find the best idle without rpm hanging. Just to not quit on my attempts to resolve this issue (Usually I don’t quit on projects like this one) I will run a few more tests that I have in mind following my theory.

Thank you all for bearing with me

General karthief said:

The hole in the throttle blade may have something to do with the problem you are having, I read the modification to the blade and what you did to make it smaller ( if I read that post correct) but there is not supposed to be a hole there. Actually I think it is bigger than 1/8” :O

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Thank you for your reply,
I appreciate your help and if that’s the case then I will just cover that opening and leave just the opening around the TB plate set by the adjusting bolt. Actually I thought the was 1/8”, but actually I think it is bigger than that as seeing on the pic. That could be the problem, we’ll see...

Thank you all again for the patience

PonyGTrider said:

Thank you for your reply,
I appreciate your help and if that’s the case then I will just cover that opening and leave just the opening around the TB plate set by the adjusting bolt. Actually I thought the was 1/8”, but actually I think it is bigger than that as seeing on the pic. That could be the problem, we’ll see...

Thank you all again for the patience

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As an update I plugged the hole on the TB blade which I’m very sure was there before.
I will set the throttle base idle speed using a 0.010” feeler gauge until the stop screw touches it and then give one and a half turns, set the TPS to 0.98 Volts. I will use the modified IAC valve (Gaskets in between the solenoid and valve body No free flow thru the valve ports when the valve is unplugged), and timing spout disconnected.
I will set the idle when the engine is at OT. In case the engine cannot run that base idle 625-650 then I will open more air by using an aluminum bypass spacer with two set screws installed in between the TB and the IAC valve. Reconnect everything and take it out for a test.

I will post the results from this test and decide if I will just keep using the IAC restriction plate with a smaller hole.

Good luck to me

nickyb said:

How did it go?

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Well didn't have time to do a road test up until now. I just came back with some inconclusive results.
In order to set up my based idle with the modified IAC valve (Gaskets in between the solenoid and the body) which keep zero air bypassed thru the valve with no power, I had to open one of the two set screws at the air bypass plate in between the IAC and throttle body. After I set the idle RPM I plugged the distributor spout and the IAC and the idle speed was nice at about 750 rpm and that's the way I left it. When I took it for a test ride the RPM's were dropping nicely from shifting acceleration to neutral to fully stop, but then all of a sudden it started doing the same hanging RPM around 1.2 K to 1.5K, then My idle got higher to around 1K. Came home and without shutting it off I turned the set screw at the bypass plate to fully closed. The idle came down to around 750 RPM and then took it back to test.

A little better results this time, the idle didn't change by much. The RPM"s were dropping to the set RPM really nice and the hanging RPM at neutral when cruising was at around 950 to 1K. Came home and idle was consistent at around 750.

So for today I'm done with this test. Tomorrow I will start the engine bone cold and see how the RPM behave thru the warm up cycle. My prediction is that it will be hard for it to idle properly until it gets warm but will see tomorrow. So far the best results still using the restriction plate with an unmodified IAC but will find out soon.

PonyGTrider said:

Well didn't have time to do a road test up until now. I just came back with some inconclusive results.
In order to set up my based idle with the modified IAC valve (Gaskets in between the solenoid and the body) which keep zero air bypassed thru the valve with no power, I had to open one of the two set screws at the air bypass plate in between the IAC and throttle body. After I set the idle RPM I plugged the distributor spout and the IAC and the idle speed was nice at about 750 rpm and that's the way I left it. When I took it for a test ride the RPM's were dropping nicely from shifting acceleration to neutral to fully stop, but then all of a sudden it started doing the same hanging RPM around 1.2 K to 1.5K, then My idle got higher to around 1K. Came home and without shutting it off I turned the set screw at the bypass plate to fully closed. The idle came down to around 750 RPM and then took it back to test.

A little better results this time, the idle didn't change by much. The RPM"s were dropping to the set RPM really nice and the hanging RPM at neutral when cruising was at around 950 to 1K. Came home and idle was consistent at around 750.

So for today I'm done with this test. Tomorrow I will start the engine bone cold and see how the RPM behave thru the warm up cycle. My prediction is that it will be hard for it to idle properly until it gets warm but will see tomorrow. So far the best results still using the restriction plate with an unmodified IAC but will find out soon.

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Hi you all.
I think I proved my theory regarding this issue.
If any of you want the details of the modifications I made to correct the outlined problem, just go to my updates from the beginning.

The results of this last test were really satisfying. At first I thought my idle was going to suffer but I have to say I was wrong. After my previous test I had my doubts but as the ECU re-learned all the parameters after the modifications everything seems to be running not perfect but to a point I'm willing to leave it like that.

First start from a bone cold engine the engine reved to about 1,500 and three four seconds dropped to about 1k then to about 750-800 and stood fixed there. The engine was still cold then I started coming out of the garage. no buckling or hesitation and then took off. The RPM's started hanging up but not even close to what it used to, this time will hang at about 900-950 even in neutral while rolling. when getting to a full stop wil drop to the original idle speed set ~750-800. One thing I noticed that at the end of the test run my idle has holding to about 900 so I adjusted one set screw at the idle bypass plate. I would be satisfied if my idle was at 900 based on the mods I have, but I decided to bring it down to prove myself that I can manipulate that idle speed back and forth at will and I did. No restriction plate and it is working nice to my like.

So there you have it, all the details are in the thread if you like to try it. In case some undesirable or unexpected weird things happen I will reply on this thread with an update.

Thank you guys