Can boost leak at throttle body cause idle surge?

[jshuman]

I recently had at missfire in cylinder one and the car was down for a while getting that fixed. It no longer has a missfire after replacing injector seals and fixing a few boost leaks. There was one boost leak that I am not sure how to fix. It is coming from where the throttle cable attaches to the throttle body. I have read tons of post trying to figure out if this leak could be causing the 1000-1500rpm idle surge i am having. Is that possible? If so do I need to replace the shaft seals? I know the ISC is a pretty common cause of idle surge on the 1g motors, but I thought the leak might be the cause. Also, the surge started after i started the car for the first time after being down for two weeks and having the battery off. I drove if for a while then shut it off and strated it again, and the surge was gone. Then the next night (last night), the battery was not secured properly in the trunk and rolled over pulling the cables off. I reattached the cables, put the tune on again with DSMlink and the surge came back. This time is hasn't gone away. Am I overlooking something simple? All the vac caps on the TB are secure. Any help would be really appreciated.
Thanks,
Justin

 

[jshuman]

I no longer have the idle surge. It has done this everytime i have the battery disconnected. The idle will surge, but after I drive it for a while it stops. But now the idle stays at about 1500rpm. What should I do or check? Thanks.

 

[dsm_racing]

I would replace the seals in the tb. It's not hard to do. If that doesn't fix it at least you've eliminated a variable and fixed a known boost leak.

 

[Turboeagletalon]

if he did a boost leak test. he would hear the air excapeing from the throttle body.

 

[Darknight968]

grab where you cable connects to ## tb and try moving it if it moves your seals are shot. this is the same probelm i had it sux'd so i replaced it and the car runs like a champ.

 

[Darknight968]

also i believe a boost leak would cause you to surge slightly. i had the same problem where it would surge then when i drove a round alil bit it would disappear. its cause i was moving the tb so it would come and go. just check it out and fix it. like they said it would deffinately eliminate this as a problem.

 

[jshuman]

Thanks guys,
I will mess around with the cable tonight and see what happens. I will put up what I find out tonight.
...Where can I get those seals? Satan had no idea what I was talking about.
Thanks again,
Justin

 

[jshuman]

Well I checked the cable for movement today. It did not move at all... in and out or side to side. But that is where I could feel and hear air coming from when I did the boost leak tests. Could the seals be bad anyways? Also, as far as the high idle goes, should I try cleaning the TB?

 

[Turbo Talon 111]

if you can hear air coming from the seals when you move they shaft during a boost leak test then yes you should replace them. Either extreme motorsports or mach V motorsports sells them for $10 but I forget which one sells it. VFAQ has a writeup on replacing them. I couldn't find the seals the way VFAQ mentions to get them so I just bought mine from one of the places I mentioned. While you have it apart clean it really well. Just don't use abrasives on either the inside or outside.
I would also check the resistance of the ISC as specified in the manual. If one of the circuits in there is going bad that will also cause an intermittent surge.

 

[jshuman]

Thanks for all the help guys. I used the vfaq suggestion about using the old seal casings with new o-rings. The replacement went extremely well, and the system held 25psi with no boost leaks. Here is the problem: my high idle is STILL haunting me! I thoroughly cleaned the throttle body while it was apart, so I am positive that it has nothing to do with the throttle plate staying open. Also, while the TB was off of the car, I tested the ISC and the TPS. The ISC coils checked out at around 29.4 ohms each which is in spec according to the vfaq. When we adjusted the tps, we got .946 ohms closed and about 5.14 wide open. The vfaq said it should be .9 ohms closed and 5 ohms open. Am I out of tolerance on that?
The idle is sitting at about 1500rms now. We tried adjusting the biss but the idle would not drop so I put it back where it was before. Am I overlooking something simple here? What is causing this rediculous idle. Of course, any help is appreciated.
Thanks,
Justin

 

[jshuman]

Also, I forgot to add the I have DSMlink. I found a little information about how the ISC needs to be reset and you have to use a scanner to do that. Will dsmlink work.

 

[Turbo Talon 111]

I have never heard anything about the ISC needing to be reset. If you have a manual, check the specs on the TPS. It gives a range for two differant settings. Make sure you are within those specs. Next I would disconnect the cable from the TB and use your logger with the car not running to check that your TPS is set right. I would be that is where your problem is. Link can show you it in percent and voltages. The Wiki I believe lists what you want to see in voltages. I'd tell you but I don't remember off the top of my head. Percentage wise though, you want it to be sitting at 0 and go to 100 when you open the throttle by hand. The reason I say to do this by hand without the cable attached is so the cable is not a variable. The only other thing to consider is to make sure the throttle plate doesn't stick. That is the problem I had when I first tried rebuilding the TB with o-rings. I couldn't get any the exact right size and so it stuck a little bit.

 

[jshuman]

I really appreciate the info. I am getting ready to try that out so I will post up what I find out. As far as the o-rings, I used the exact ones listed in the vfaq, and they seemed to fit just fine. I also opened the throttle plate different amounts many times before I installed it to see if it was closing properly. I will check it again though, just to be sure.
thanks again

 

[jshuman]

Ok I checked the throttle plate again and it is closing completely and isn't sticking. I am also going to adjust the tps again tonight and try to get it dead on with the vfaq numbers. Is anyone familiar with adjusting the tps using DSMlink? I have read where people do it that way, but I havent figured out how to do it myself. The dsmlink guide does not go into much detail on that subject, and I have found no info on the dsmlink forums.

 

[jshuman]

I logged a few things with dsmlink to try to help give me an idea as to what the problem is. I checked tps volts and throttle position and a few others. The volts were right within specs. THe throttle position read 3% when closed and 97% when wide open. Using the raw throttle position info, I calculated for the tps adjustment procedure in the dsmlink manual and on the vfaq. I ran the numbers over and over to make sure I did it right. But when I checked the throttle position again, it read 100% when wide open, but 4% when fully closed. (and that was with the throttle cable detached so that was no a variable) The idle was still setting at 1500rpm. I tried adjusting the biss down to 900rpms again ( the idle rpm set on dsmlink). This time it did not raise back up. It is a little unsteady, but much better than 1500! The problem now is when I go WOT, it feels weak. This is frustrating considering that it ran better than ever before last week before the battery got disconnected.

Also, I did run another boost leak test just to tripple check, and it is still holding 25psi solid. When I did that test run yesterday, I was getting a cel under WOT, and it would go away as soon as I let off the pedal. Is that knock related? I have a 24x12x3.5 front mount with hyperdrive alcohol injection. Should I be having knock issues, or could it be a timing thing?

And one last thing, I am not sure if my alcohol injection is working now. It has not been using hardly and alcohol. Like one cup every couple weeks- that could just be loss from evaporation. Is there a way I can test the pump?

Sorry for being so lengthy... but I can not get this figured out.
Thanks in advance,
Justin

 

[Talesin]

Did you remember to ground both check connectors before messing with the BISS? Biggest problem most 1G guys have is forgetting to ground both and get the ECU to go 'hands off' on idle. Not sure of the procedure for 2G guys, but I'm pretty certain it's not just going after the BISS as the first step.
Next, check for a vacuum leak. Anything from the TB to the intake manifold to head gasket could be leaking... and the prime cause of idle surge or a high idle is a vacuum leak. What does your boost/vac gauge read at idle? Should be right around 20in/Hg at idle, at sea level.
Spray a little carb cleaner at a suspected leak, and if the idle goes up, you may have found (one of) your leak(s).

 

[jshuman]

thanks Talesin,
No I didnt ground for the BISS because I read where you dont necessarily have to when you have DSMlink. This wasnt the first thing I tried though. I started with leaks first. I put new seals in the throttle body and tested the ISC and TPS. I am sitting right at 20in/hg, so I don't think it is a vac leak. I have also done the carb cleaner test, and it didnt affect the idle. I did a comression test too so I dont suspect a head gasket.
I think part of the problem is with the TPS adjustment on link. When I enter the scale and offset numbers, the scale percentage stays entered, but the offset goes back to 0 after I click ok. The offset is supposed to lower my raw throttle position to around 32, but it is staying at 40 because it wontn retain the value I enter. If any one has had experience with this, I could use some help.

 

[Talesin]

Well, might be better to log into the DSMLink forums and ask there? I have Link sitting on the shelf.. still have to find a place to socket the ECU locally, so I won't have any downtime. May want to try doing the stock BISS adjustment routine anyway, just to be sure, if turning the BISS doesn't alter the idle without grounding anything. The people telling you that might have bad information, or you might be getting a fluke response for some reason :3

I'd expect more of the stock idle surge problems, and yeah, doesn't sound like you have a vacuum leak if you're right on 20.
Er... stupid check, your idle sensor switch wire is connected, right? Mine was taken off when I had the engine re-done and they forgot to plug it back onto the TB spade connector, so the car would sit at 1K-1.5Krpm constantly unless I hooked my toes behind the gas pedal and lifted a bit.. would drop a little, but not much. Popped the wire back on when I noticed, boom, 750 on the nose and decel at 1K when coasting down in neutral.

 

[jshuman]

No my idle switch is not connected. I looked into that and everything said that it was not need since I have a 6 bolt in a 95 with a 95 ecu. I guess the idle switch is built into another sensor... the TPS i believe. I will double check that though

But I will post the TPS adj question in the dsmlink forums.
Thanks again

 

[AndrewD5418]

Get a logger and check to see if your TPS is functioning correctly at idle. Mine was dying and made me idle surge untill my engine was warm. It also threw a cel recently. I noticed that mine wasn't working right because I was off of the throttle, and it was at 0.0%. I press about 25% throttle on the pedal and it still said 0.0.

 

[jshuman]

I had a fellow DSM owner help me find out why I was pulling a cel under WOT. We went out with the DSMlink to try to pull the DTC for the check engine light. I went wot in 3rd and sure enough the light went on. We ran DTCs and it gave the code 0120 : throttle position circuit malfunction. I am going to search now for what that might involve. I am going to try to manually adjust the tps tomorrow after I get off work while streaming with DSMlink. I read that the closed raw throttle position should be around 32. I am at 40 now so I am going to try to gete it close to 32 and see what happens. I am open for any suggestions at this point.
Thanks for the help!

 

[jshuman]

I adjusted the tps manually until my raw throttle position on dsmlink read 32. When I was doing that, I am almost certain I heard the isc plunger move. I think it may have recentered. Now the idle is right about 900rms, and pretty steady. I think after a little more fine adjustment, everything will be ok. I am still getting the p0120 cel under wot, but I think I can get that worked out.
Thanks again to everyone who helped out!
Justin