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S90 76MM TB Issues?

B

Beefman147

Messages
26
Hi,

I am just wondering if there is any straightforward way to adjust the sensitivity of the throttle on a DC5? My motor has the 76mm S90 throttle body on it so it may be related to this but the car seems to be very sensitive in regards to the throttle being on/off. It can make it jerky when changing gears or taking off, particularly with the stiffer clutch.

Even at idle if I try to steadily increase revs to say 3k it can be difficult and it will just jump up to 3k. I hope this explains the issue. It isn't an overly big deal but it would make the driving of the car nicer if this was smoothed out.

I am debating reverting back to the OEM TB and just using a silicone reducer to retain the current intake on the car. (76-63mm??) Would this be ok to do without running issues?

Cheers in advance.
 
Is it mapped, if so who mapped it?

Gains through a large throttle body are minimal at best and the larger you go the better mapping it requires, simply slapping on a base map with a tweak like most places do isn't going to cut the mustard.
 
No it doesn't have an ECU so it must just be on the standard map. I believe the larger TB is causing the issue but am just keen for someone to confirm before I change it for an OEM one. 76mm to me seems massive considering its on the standard inlet manifold too. It was fitted to the car already before my time.
 
Well yes you can't put such a large throttle body on without it being properly mapped. I'm also fairly certain that most mappers in this country wouldn't be able to map it correctly anyway and unless you have a mods list as long as your arm, the gains would be negligible. Putting an OEM one back on will cure the issues.
 
Chris. said:
Well yes you can't put such a large throttle body on without it being properly mapped. I'm also fairly certain that most mappers in this country wouldn't be able to map it correctly anyway and unless you have a mods list as long as your arm, the gains would be negligible. Putting an OEM one back on will cure the issues.
Click to expand...

Thanks Chris. I have sourced an OEM one at decent money so will fit it and report back. I'll order a silicone reducer as the current intake is obviously the same bore as the TB. Surely this should be fine to run with? Also, any input on how handy it is to change the TB? It isn't my daily drive so don't mind tackling jobs like this if they are straightforward enough.
 
You should be able to change the throttle body yourself, it takes around an hour. Remove the intake hose, there are then 4 bolts to remove and a few plugs, Remove all the plugs first, then the bolts and it should come free from the intake manifold. Then reverse the process. It may be an idea to get some loctite for the bolts before you put them back in and I'm sure a quick Google should reveal their torque settings. Depending on how long the current one has been on for, it may be an idea to order a replacement gasket, Cox Motor Parts or Hendy Performance can supply them.

I'm not sure about the outer diameter difference of a 76mm vs standard plenium. I know with the Spoon 70mm for example it's just the OEM one bored out on the inside so the outer diameter is the same.
 
Might be a silly question this......but I am going to fit this standard TB after work today and was just hoping to clear something up. The standard TB doesn't have the TPS attached so I will have to switch this over. Will this be straightforward as looking at the sensor the bolts holding it in place to the S90 look tamper proof. Also when I do get it switched over I am guessing it will need adjusted/calibrated. Will this be something I will be able to have done by driving the car to my local car electrics place and getting it adjusted to the correct voltages there?

Thanks
 
I haven't removed a TPS before, I understand it's at the back of the TB itself. You may have to calibrate it once moved over, if you do a Google there are a number of results which explain how to do it.
 
TPS' need to be calibrated when moved, unless you get very lucky, and she won't like driving with it uncalibrated. Have you got an ODB scanner or a multi-meter? If you can fit the TB you'll be able to calibrate a TPS no problems.
 
I don't have a multimeter but I could pick one up from Halfords or the likes if it is a straightforward job to calibrate the TPS? I definitely am removing the S90 TB as these have been known to cause issues. The standard TB I am replacing it with just needs the TPS switched over so and calibrated. I'll probably give the IACV on the standard one a clean just to be sure.
 
As above, if you're mechanically minded to be able to swap the TB's you'll be able to do the TPS without much trouble. Find a good guide with pics online and you'll be able to crack it in no time. Cheapo multimeter are less than a tenner at halfrauds.


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Have it all pulled apart now. Was fairly straightforward. However I did find that on the S90 TB it had a blanking plate over the 3 IACV ports which I found odd.

For now I am going to swap the map sensor on to my TB as it didn't come with one and refit and take it from there. Its bucketing outside now so probably be a job for tomorrow.

Is there any particular way the TPS reattaches as I can't recall what way it was pointing while dissambling?
 
It can only go two ways, connector pointing up or down, so you've got a 50:50 chance :D logical place is pointing down, keeping the wiring harness short, but I guess technically it could go either way if it doesn't have internal stops, it's only a variable resistor in a fancy casing. You'll be able to see on a multimeter quite quickly if the resistance goes through the right range in which ever position you try first.


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As things stand, put the TB back on and connceted the TPS loosely. It was raining by this stage AGAIN! So i fired the car up quickly out of curiosity and it was revving at 2k stable....this is a change from what it previously used to idle at (around 5-600 when cold).

I'll have to leave it until tomorrow but would this be the TPS being out causing this? Would the fact that it had no intake hose over the tb as all affect this idle? I'm thinking fingers crossed once I set the TPS to the right voltage everything will be fine.
 
Is the DC5 drive by wire?

It's probably a combination of the three things you've mentioned, stone cold engine, no air filter/box and TPS not quite right.

Edit: And the ECU needs to re-learn the idle characteristics with the new TB.

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Honestly not too sure on that. I'm hoping you are right about that. Ill have a go at calibrating the TPS tomorrow and hopefully have only positive things to report back. I'll be over the moon if it idles better from cold and drives smoother as it was much too jerky before removal.
 
Is there a throttle cable or is it controlled electronically haha? Got no idea about a DC5.

Is is possible for a TPS that's out to cause all sorts of issues including jerkiness, but if it was really bad there's every chance you have other issues too.


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