Help figuring out a throttle issue

[thewatcher101]

When I am driving on the freeway around 65-70 and modulating the throttle to keep it at that speed - the rpm gauge would suddenly drop come back up drop and come back up - the car does not stall. It would do this for a 30 seconds or so and then won't repeat itself. It never happens around city only at cruising speeds on the freeway.

The only thing I can think of that would cause this is the throttle body is shutting.

Would adjusting the idle screw or the throttle cable the best way to deal with this issue.

My throttle cable has a bit of play in it because it is a bit long.

[Satisaii]

Could be something in MS. Datalog it.

[thewatcher101]

it only happened after the SC install the only electrical thing that change was the removal of the TPS which the MS never took a reading from.

that is why is suspect it to be that issue -some have suggested that this is a common problem with a bad ground - but a bad ground would have shown itself before this

time to do more logging

[MX-Drew]

It can not be the throttle body as the engine will still be turning through the gearbox / back wheels unless you are saying the back wheels lock up or you slow down then speed up again.

It is more likely to be a bad ground or signal to the gauge.

Does the engine sound like it drops in revs?

[Steve in VC]

I assume the throttle is still mechanical (cable from pedal to butterfly). It isn't changing position without your foot doing it.

If the engine slows, the fuel is being pulled or spark timing changed. I assume that is information that will show on the data log.

If the car isn't slowing, does the MS source the tach? If so, could be a lose connection there.

[Tom @ Fast Forward]

The RPM gauge (tachometer) changes rapidly but, does the engine drop also or just the gauge?

[thewatcher101]

I went to clean the ground today - the one that is near the brake booster. I driven the car today and it has yet to repeat the problem.

When the rpm gauge drops the engine rpm (i don't think can drop that fast) - the needle pretty much bounces up and down - but the car stutters a little

it only happens when i am on the highway in fifth and I am very light on the throttle to maintain my speed - it has never happened during acceleration or in city driving

[Godless Commie]

Looks like a wiggle test is in order.

My feeling is, something was either not tightened, or not plugged in snugly during the install.

Sounds too much like a loose ground to me.

Idle the car and wiggle all the electrical wiring, connections, etc. A stumble will be the telltale sign.

[Tom @ Fast Forward]

I'm with GC.

[Godless Commie]

I'm with GC.

I am SO proud.

[Tom @ Fast Forward]

Hey, us commies have to stick together. If I have to explain, you have not been paying attention. ;)

[Godless Commie]

Shhhhhh, comrade...

[thewatcher101]

thank godless commie - i figured it out it was my IAC rig that was causing the issue - good call

[MX-Drew]

thank godless commie - i figured it out it was my IAC rig that was causing the issue - good call

Can you please explain exactly what the cause was as I would like to understand how the IAC caused this problem.

Cheers.

[Godless Commie]

You are very welcome, comrade.

(Everyone on the forum will be a comrade soon if I keep this up..
Good thing I am a few thousand miles away from the DHS :rolleyes: )

[thewatcher101]

When I did the install on my 91 with a 97 engine - I used a 97 IAC because my IAC was pretty much stuck to the TB and the kit was for a 97 engine so the bracket also was there. The plugs on the IAC did not fit so I had to make a connector myself - the connectors end up touching each other during vibrations which caused a random bouncing drops.