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Hi,
My mechanic removed the A.I.R pump, installed OBX headers and deleted the EGR as well.
Now, before these changes, the idle was fine, around 700-750 RPM.
When I got back from my mechanic, I noticed the idle (parking) become way too high, approx 1300 RPM.
What can cause that? bad sensors? all vacuum pipes looks ok. MAF looks connected. I haven't check if the O2 sensor is attached.
Thanks.
IDK. Who is your mechanic working for and where is your location? How to help you would be to scan the car and see what the IAC is doing. For some reason you now have a much higher RPM. Maybe a hose is loose or put in wrong. Maybe you need to adjust your IAC. IDK how to adjust it reliably without a Tech1 scanner since you are in the year most scanners do not work. Could he have disconnect a temp sensor wire? Could a hose be leaking? Could it need more adjustment in the IAC? Hard to say without seeing data.
No, the FSM way sucks since it assumes everything is in spec which something obviously isn't.
Why did he delete the egr? Did he use a plate on the manifold? Possibly a vacuum leak has started. Removing the egr in a car that has a stock tune can cause pinging. He should have left it alone and just installed the headers and deleted the air pump.
IDK. Who is your mechanic working for and where is your location? How to help you would be to scan the car and see what the IAC is doing. For some reason you now have a much higher RPM. Maybe a hose is loose or put in wrong. Maybe you need to adjust your IAC. IDK how to adjust it reliably without a Tech1 scanner since you are in the year most scanners do not work. Could he have disconnect a temp sensor wire? Could a hose be leaking? Could it need more adjustment in the IAC? Hard to say without seeing data.
No, the FSM way sucks since it assumes everything is in spec which something obviously isn't.
remember.....scanning 85's is somewhat futile as the car can only be scanned in field test modd which alters the state of ghr car. in this case though, it would help. the iac is most likely going to be fully closed while trying to reach the 1000rpm that is field test mode. that confirms vac leak.
remember.....scanning 85's is somewhat futile as the car can only be scanned in field test modd which alters the state of ghr car. in this case though, it would help. the iac is most likely going to be fully closed while trying to reach the 1000rpm that is field test mode. that confirms vac leak.
Is there any way to get live data without corruption? Or do you need a tech 1 scanner to do that?
Is there any way to get live data without corruption? Or do you need a tech 1 scanner to do that?
to be honest im not sure that even the the tech 1 can scan the 85 without initiating the "field test mode". off the too of my head it does a few things like advance timing, and bumps idle hold 1000rpm. driving around in field test mode was not recommended. i sold my 85 so my memory is pretty fuzzy. the 86 and later can communicate without the "state" of the car being altered.
Hi,
I checked this morning. I check cables of the TB. pull out and pull in.
After cold start, I waited approx 7 minutes.
The RPM was ~ 650/700.
Check also with Actron scanner, no error codes.
Hi,
My mechanic removed the A.I.R pump, installed OBX headers and deleted the EGR as well.
Now, before these changes, the idle was fine, around 700-750 RPM.
When I got back from my mechanic, I noticed the idle (parking) become way too high, approx 1300 RPM.
What can cause that? bad sensors? all vacuum pipes looks ok. MAF looks connected. I haven't check if the O2 sensor is attached.
Thanks.
Hi
when i first got my vette i removed the air pump disabled the EGR and fitted headers, it did not change the idle still at 600 rpm.
Is the EGR valve still fitted to the car? removing it and putting a block off plate will allow exhaust in and cause high idle or stalling?
You only have to disconnect the solenoid valve or vacuum hose to disable EGR.
Perhaps he fiddled with the idle stop screw, if he did you will have to do a base idle setup procedure.
Any vacuum leak will raise the idle, you should only have 1200 rpm for a few moments on start then drop back down to 600.
I would go elsewhere he obviously doesnt know anything about C4s
when i first got my vette i removed the air pump disabled the EGR and fitted headers, it did not change the idle still at 600 rpm.
Is the EGR valve still fitted to the car? removing it and putting a block off plate will allow exhaust in and cause high idle or stalling?
You only have to disconnect the solenoid valve or vacuum hose to disable EGR.
Perhaps he fiddled with the idle stop screw, if he did you will have to do a base idle setup procedure.
Any vacuum leak will raise the idle, you should only have 1200 rpm for a few moments on start then drop back down to 600.
I would go elsewhere he obviously doesnt know anything about C4s
Hi,
The EGR is still there but disconnected.
As I mentioned above, I disconnect and connect the IAC switch.
I know the mechanic checked the TB while he installed the OBX headers.
Another thing I noticed is bad connector of the knock sensor. it seems broken.
I ordered it yesterday. I assume I'll get it in two weeks and replace it.
Can a bad connector of the knock sensor can do the symptoms I described?
i'm subbed here because if somebody can figure out how to scan and 85's EC you without forcing the car into field test mode corrupting the condition that most people are trying to scan for, I'm interested! I had a 1985 and I spent hours and hours and hours and hours and hours! Doing this and there was no way to do it.
Can a disconnected knock sensor can cause high revs?
my connector is broken. When the engine is cold I can put it in place but it isn't hold.
When I start the engine after a few mins the revs for parking is around 800-900. When I start to drive and stand in a traffic light (D not parking) the revs are ok (550 - 700).
After driving a while lets say 30-40 mins I noticed when I put to parking, the revs can reach 1200-1300.
the vent is working and the temps are normal.
i'm subbed here because if somebody can figure out how to scan and 85's EC you without forcing the car into field test mode corrupting the condition that most people are trying to scan for, I'm interested! I had a 1985 and I spent hours and hours and hours and hours and hours! Doing this and there was no way to do it.
The knock sensor being off won't cause that issue. The wire is cut on mine and it runs fine.
I noticed you said in the o.p. that you hadn't checked if the o2 sensor was installed. Did you ever confirm it's there and sealed properly? An exhaust leak near the o2 would do ugly things to your mixture.
Codes on an OBD1 are pretty much worthless. When these cars were new we used to joke that if your check engine light came on you should do just that...check to see if it's still there. If it is, keep on driving and ignore the light.
I think the key here is that it is temperature related.
is it possible it idles low when cold just cause it's running kind of crappy?
does it start okay (my '85 cold starts when I just touch the key...click-vroom). Idle smooth?
Hi,
The EGR is still there but disconnected.
As I mentioned above, I disconnect and connect the IAC switch.
I know the mechanic checked the TB while he installed the OBX headers.
Another thing I noticed is bad connector of the knock sensor. it seems broken.
I ordered it yesterday. I assume I'll get it in two weeks and replace it.
Can a bad connector of the knock sensor can do the symptoms I described?
If the sensor in the picture is the one you are referring to as the knock sensor, I believe you are mistaken. The sensor in the picture is located in the cylinder head and is one of the coolant sensors I believe.
On my 86, the knock sensor is installed in the cylinder block drain plug location on the passenger side close to the starter motor when viewed from the bottom.
That being said, if the symptoms are temperature related, and you found a broken connector on a temp sensor, you may be getting warmer (pun intended)
I don't have any temprature issues at all.
Regarding the O2 sensor, I just crawled and checked. The sensor is connected. Currently I cant verify that the sensor itself is well installed (screwed).
I don't have any temprature issues at all.
Regarding the O2 sensor, I just crawled and checked. The sensor is connected. Currently I cant verify that the sensor itself is well installed (screwed).
How do you know this? Have you been scanning to see what the ecm sees?
01-02-2018, 02:55 PM
1985 after air pump delete + headers
